I'm not a fan of playing "the long game" if that means losses in the regular season given that that comes back to bite you big time with lower seeding in the playoffs.
Road wins in the playoffs are extremely difficult and it is foolish to think that 'the switch' can be flipped to make up for losing home court advantage.
The Celtics have roughly a 33% W-L record on the road in the playoffs and it's been worse (~25%) in the Brad Stevens era. So regular season losses are indeed costly in the playoffs.
If there truly is some sort of motive to 'teach a lesson' by not making in-game / in-season corrections then that seems absurdly stupid to me. It shouldn't take a season of floundering against the same problems to learn the 'lesson' and the long-term cost (home court advantage in the playoffs) is a heavy price to pay for such a 'teaching method'.
I just don't buy that this is intentional in any way. And if it is, then it's inexcusable. Regular season games DO matter, both for the playoffs and for the fans paying $$ to watch them.