It's not delusional to think the C's will make the playoffs. The East is very weak, with only the Pistons and Cavs possibly being any better than last season. A Celtics team with Rondo, Bradley, Green, and Sullinger is just decent enough to get around 35 wins, which might be enough to grab a #8 seed. Winning the championship is a whole other story.
As for the bench, I'd like to think the C's actually have one of the better in the league. Brooks, Wallace, Humphries/Bass, and Lee are all decent, most of whom can be starters on other teams. It will be interesting to see if Wallace can rejuvenate.
Of course the gaping hole in this team is the center position. If there's any reason to count out a playoff appearance, it's that. So far our center situation is either Fab Melo, Faverini, or an undersized PF.
I'm not sure I like the OKC analogy. Yes, they sucked and subsequently built through the draft, but you gotta understand how rare it was for the Thunder to hit gold on three consecutive lottery picks. They traded Allen after they secured the #2 pick, which guaranteed them a franchise player. Prior to that, they were still trying to win games with Allen and Rashard Lewis. They finished the season with the 5th worst record while winning 31 games. I'd say 31 wins is a good ballpark estimation for the C's this season.
That's why I'm against tanking - you can still try to win yet ultimately lose enough games to secure a high lottery pick.
Anyway, back to OKC. It's fun and all to use them as an example, but like I noted previously, their situation is extremely rare. Either they got really lucky or they have really good scouts. It's easy to hypothesize the C's tanking and grabbing players of Durant, Westbrook, and Harden's caliber, but more often than not their drafts will turn out like Memphis, Charlotte, or Washington.
For example, much like OKC, Memphis also had #2, #3 (trade), and #4 picks around roughly the same time. Those picks turned into Hasheem Thabeet, OJ Mayo, and Mike Conley. Interestingly enough, Conley is a result of the Oden-Durant sweepstakes draft, the season in which Memphis finished last in the league, only to get the 4th overall pick and miss out. Ouch.
The good news is Memphis actually built a winning tradition. Not through those three players though, but through trades, free agency, and prior draftees. Randolph, Marc Gasol, and Tony Allen really helped turn that franchise around.
So if you want to use OKC as an example, it's only logical to use Memphis as well. You can also look at teams like the Bobcats, Wizards, Raptors, and Timberwolves, who despite finishing near the bottom season after season, have not been able to draft more than 1-2 NBA starting-caliber players.
Not saying Ainge has the ineptitude of those GMs, but it's more common to draft players who'll never amount to much than superstars like Durant, Westbrook, and Harden.
Oh, and if Ainge kept the #5 pick, it's very possible he would have drafted Yi Jianlian.