I haven't read through the whole thread yet, but this is my two cents. I think we need to distinguish two things here.
One is the actual tanking, meaning finishing last on purpose. I have no problem with that. If you argue against tanking, you would have to consider that probably the best approach to start the game is to invest into your arena first while not taking on too much salary.
After all it is each manager's decision how he wants to run his franchise. Get a couple good draft picks to build around, buy some talent and train them or buy already good players. Everyone has to decide on his own if he wants to win now, slowly get stronger or take a different approach. And there is more than one way to be successful.
Number two is the buying of high salary players for the playoffs/relegation. While I do think it is each manager's choice if he wants to push for homecourt advantage in the playoffs or accepts playing on the road, there needs to be a fix. Again, I support the idea of "tanking" and going for a 4th place finish with less salary. Manager A might have a higher salary throughout the season and finish 1st and get homecourt advantage. Thats his reward. Manager B might have less salary and finish 4th. He doesn't get homecourt, but might have saved a couple bucks along the way. There is nothing wrong with buying an extra player now. In order to prevent an abuse of that by going for a player that earns as much as the whole team, simply move the deadline for the player to be eligible for the POs two weeks ahead. Buying players is an integral part of managing and those two weeks would make up for the financial gain over the course of the season for Manager B I would assume (after all you have to consider that manager B is probably making less money from home games and merchandising). That way everyone needs to think twice before taking on a huge salary player. And if his playoff run doesn't lead to the championship he might be broke afterwards.
Another idea to somewhat balance the whole thing is giving financial bonuses for winning teams. Say each team gets a certain reward per game won (similiar to the cup rewards) and/or also a prize for the league finish at the end. Giving detailed numbers here would not make sense, since only the BB developers have insight into what the teams in different league levels earn per week.