In which schedule do you have more games against awful teams? In which schedule do you have more games against great teams? In which schedule do you have more games against the middle of the road teams?
As I said, if a schedule is 'balanced' or 'loaded' (such as the way the NFL does it) has an effect and any particular team's individual schedule for given year has to be looked at in particular.
But my assertion is that, on average, in an expanded league - all other things being equal including the total number of games played in a season (82) - an elite team will play a greater share of games against mediocre and crappy teams than against elite teams. This should follow straightforward from the math, assuming talent is similarly distributed in each era and has a similar 'average' level of talent.
It would seem to me that despite playing teams like the Sixers 10 times, that Boston in 65-66 in fact played a pretty darn easy schedule because you balance those Sixers games with 10 games against the Knicks and 10 games against the Pistons (who inexplicably Boston had the third worst record against despite them being the worst team in the league).
THe crux of my point is not based on how many times an elite team gets to play the 'patsies'. As you point out, fewer/more games against patsies is balanced against fewer/more games against elites. The difference in an expanded league scheduled over the same 82 game schedule is that they will end up playing more games against the medium teams. And on average, an elite team will win matchups with medium teams.
In the data you posted, 5 of the 8 teams the C's would face were mediocre or worse and they accounted for 50 of the 80 games. 30 of 80 games, or 37.5% were against teams with 45 wins or more.
Anecdotally, the 92-93 Bulls (just picking a random Jordan championship) played just 23 of their 82 games against teams with 45 wins or more (28%).
To do this right, of course, we'd have to compare a bunch of seasons in each era, but I suspect that pattern is the norm. In an expanded league, an elite team will play a smaller share of it's games against other elite teams. Thus it will tend to rack up more regular season wins (since we assume other elite teams have a ~50/50 chance against them while lesser teams do not).
This doesn't mean the talent is deeper or thinner in either league.