Chriss and Len are two entirely different players, Len is more of a defensive old school center and Chriss is a very athletic but undersized PF right now. Len has looked good this year but a number of people wanted to move on shortly after he was drafted and haven't really changed their mind. He's at least as good Chandler is and we're paying him 15 million a year. Chriss will take time to develop but there is a chance he ends up being a SF in the NBA, the main reason he's our starting PF is out of necessity, not skill. I think Bender is more NBA ready but the front office and Watson view him as a better player overall, now and down the road, so they're not going to shake his confidence by starting and playing him against superior competition every night.
I don't know what you base that on but Chandler is the better player and it isn't even close. Chandler is better at literally every facet of the game and our splits when Len is out there compared to Chandler are worlds apart. We're getting killed when Len is on the court to the tune of -11 per 100 possessions, with Chandler out there it is -2.
Len is a terrible offensive player and on defense, while he can make some plays, overall he is really lousy, he just gets lost out there, frequently meandering away from his man. His biggest defensive problem is his fouling. Even if we got rid of Chandler, Len fouls at such a pace the if given starting minutes he'd foul out nearly every game.
I do agree that Chriss may be better off in the long run as a SF.
And I also think Bender is the better player of the 2. Bender's individual stats are not good right now but when he is on the court things seem to go well. He seems to have a good feel for how to move around both on offense and D. And going back to Len... that is his biggest problem, he does not seem to know where to go on either end, a bad instinctual player.
He isn't trash, given a few more years he could be a decent reserve but there is nothing about him that suggests he is or is going to be someone who should be a regular starter.