I don't think Boston beats Toronto if those games are in Toronto. History bears out just how infrequently Boston wins in Toronto and the teams were obviously pretty evenly matched. So I think Miami, Milwaukee, and Toronto were all better teams in the east last year. Miami is struggling this year, but I think they will still be as good as they were last year when the playoffs roll around. Toronto is obviously not as good as they were, but are still in Boston's same general range (they are 1 game back). Brooklyn is certainly better than Boston (at least from a playoff perspective if not regular season as well) and Philadelphia may very well be (they will clearly finish with a better record, though it is yet to be seen how good they will be in the playoffs). So Boston is the 4th, 5th, or 6th best team in the East and was always going to be. They certainly could end up with a better seed than that, as health plays a big part in regular season records (though Indiana could finish as a higher seed also).
Teams that are consistent contenders quite simply have top end talent that is better than the C's have. The C's have been a very good regular season team, but in the playoffs you just need the uber elite guys to have any real shot at winning championships. Even the Bucks, who have the 2-time defending MVP, haven't even made the Finals, because the supporting cast around Giannis just hasn't been good enough and their supporting cast has been better and deeper than Boston's. Top end talent wins and Boston quite simply doesn't have it. Hopefully someday Tatum elevates into that class and Brown continues to improve so that he can be a sufficiently talented #2, but until that happens, Boston isn't a contender.
Two All-NBA caliber players is top end talent. Any definition of top end talent that excludes Tatum and Brown, at this stage, is simply an obviously flawed definition.
You also completely skipped right past the point I made that the Celtics were a top 5 offense and defense last season. That's another rock solid indicator of being an elite team.
You can spin alternate histories as much as you like -- I can't argue with you, because you're stating an opinion that isn't based in anything that can be proven or disproven. I would just point out that I haven't seen you similarly discounting what other teams (like the Lakers or Heat) did in this most recent post-season on account of the neutral court. For whatever reason you only apply that skepticism to the Celtics.
It's one thing to say the Celtics are not in the top tier of teams in the league -- what I would call the "title favorites." I would agree with that. They're not in the same category as the Lakers or Clippers. They don't have the same level of talent at the top of the roster as the Bucks (based solely on Giannis), Sixers, or Nets.
It's entirely a different thing to say the Celts, heading into this season, could not reasonably be considered in the outer circle of dark horse title contenders. That would include teams like Miami, Dallas, Denver, Utah, etc. The Celtics absolutely earned that level of consideration and to say otherwise requires you to completely discount what the team has done the past few years, relying on opinion and gut-level instinct rather than any concrete pieces of evidence.
Look, I don't want to make this personal, but I feel like you have always been pessimistic about the Celtics, year after year. My impression is that there's almost nothing the Celtics could do short of winning the title that would convince you to change your mind about them "not being good enough." Even so, you've been proven wrong a lot of the time about how good they are and how far they can go. So I would think that perhaps having been wrong about that would encourage some humility or doubt as to your own instincts on that sort of thing. I've been a pessimist at times myself, and I'd like to think I've recognized when my priors about the players and the team as a whole have been shown to be too negative.
But Boston doesn't actually have top end talent when looking at title winners and frankly title runner-ups most of the time.
Look at the last decade or so.
Lakers - 2 top 5 players
Raptors - top 5 player, 2 other all NBA caliber players, former dpoy
Warriors - 2 top 5 players, 2 other all NBA caliber players
Cavs - best player in league, 2 other all NBA players
Warriors - top 5 player (and 2 time MVP), 2 other all NBA players
Spurs - rising star, greatest PF ever, All NBA guard, HOF guard
Heat - best player in league, 2 other all nba player
Mavs - top 5 player, dpoy, HOF (old) guard
Lakers - top 5 player, 1 other all nba player
Celtics - top 5 player, 2 other all nba players
The Spurs are the only team that didn't have a top 5 player of the champions and they all basically had at least 1 other top 15 type player. The Spurs though had the greatest PF in the history of the game (Duncan), a HOF guard in his prime (Parker), a HOF guard at the tail end of his prime (Manu), and a rising star (Leonard). Duncan is what really sets them apart from Boston, and that is the closest comparison. Now I get it those are the champions, but what about the runner-ups.
Heat - Top 10 player, Rising Star
Warriors - 2 top 5 players, 2 other All NBA caliber players
Cavs - best player in league, 2 other All NBA caliber players
Heat - best player in league, 2 other All NBA caliber players
Spurs - rising star, greatest PF ever, All NBA guard, HOF guard
Thunder - 3 future MVP's
Heat - best player in league, 2 other All NBA caliber players
Celtics - 3 All NBA players, rising star
Magic - top 5 player
Lakers - top 5 player, 1 other all nba player
So you add the Heat, the older Celtics, along with the Spurs without a top 5 player, and arguably the Thunder, though they had Durant, Westbrook, and Harden on that team.
The reason I say Boston isn't a contender is because they don't have a top 5 player. 2 All NBA caliber players isn't generally enough. Even on teams that have a top 5 offense and a top 5 defense because when the playoffs roll around you need a guy that is a top 5 guy to fall back on. And that top 5 guy almost always needs another top 15ish player to fall back on. It is one of the reasons why the Bucks haven't been able to break through because for as good as Middleton has been, he hasn't been a guy that the Bucks could consistently rely on when Giannis needed help. There have been plenty of teams that have been both top 5 offenses and top 5 defenses that weren't really considered realistic contenders. Toronto was one of those teams before Kawhi. The Hawks 60 win season they were 6th in ORTG and DRTG (and were 4th in Net RTG and SRS), but no one thought they had a chance of winning the title and they were swept by Cleveland in a totally non-competitive series. And frankly champions are often not in the top 5 for both categories, so I just don't think it has much actual correlation to what being a contender is. The regular season is not the post season.
At the end of the day, teams almost always need a top 5 player and at least 1 other top 15 player to even make the Finals, let alone win. I certainly believe Tatum can get to that top 5 status one day (I've been pushing that narrative for years now), but he isn't there yet and until he is there, Boston isn't going to be a contender. Top end talent wins, and Boston quite simply doesn't have it right now.