I think that the incoming players are going to have to fight for minutes with an upperclassman Thiam, regardless. He's a much better player than he was last year, and should be even better next year (and without freshman-itis).
These are good problems to have, though. I'd rather be discussing which player is going to get minutes than why certain players are getting minutes.
Thiam DOES have to get better at getting open, and driving to the basket ... and he needs to get stronger.
On the other hand, he was REALLY good defensively against Bridges last night. In the 1st game against MSU, at RU, Bridges schooled Thiam a bit - he physically pushed Thiam around, and Thiam was slow and/or lazy getting around or through screens. But in this game, Thiam was much improved. Bridges was held scoreless in the 1st half, with few open looks. And other than 1 very short stretch in the 2nd half, where Bridges scored 7 points of 10 that MSU scored in that stretch, Bridges did very little. And it was MOSTLY with Thiam covering him - though a little bit of Williams, as well. For the game, Bridges was 3-10, with 4 turnovers, a much improved job by Thiam. And while it was true that Thiam himself only had 1 short stretch where he hit 2 3's (2 FT's came later in that 1st half, or in the 2nd half), Thiam with 8 points and Brudges with 11 is a good trade-off for RU, and a key part of why this game was so comeptitive.
RU will be a MUCH better team next year if Thiam develops even a little more, and is able to become a 11 ppg and 4-5 rpg player, plus maintain or even slightly improve his defensive effort. Having a 6'10" wing player who can hit the 3, hit some FT's, maybe drive to the basket even just a little, and defend is a really nice match up situation.
Plus, in re the players being brought in next year ... I am pretty sure none displace Thiam's role, not the current players we know about. Mathis would have to replace Williams, not Thiam. Carter is repalcing Freeman, not Williams. The red-shirt Johnson replaces Sa, not Thiam. Harper may be able to contribute - hopefully he will add a little extra shooting, for example - but it would surprise me a lot if Harper took HUGE minutes from Thiam ... he s only a freshman, and not quite as highly regarded as either Mathis or Carter.
P.S. Edit ... I keep forgetting about Kiss. Kiss will play some 2G and some WF. If Sanders returns, Mathis and Kiss, with Mensah as the 5th guard, will help Baker and Sanders have reduced minutes, which will mean higher defensive intensity when they ARE in, and better legs at the end of games. If Sanders does NOT return, I presume RU will add another recruit - at the guard position. At WF, Thiam will very likely start, again. Kiss and Harper will vie for back-up minutes. Thiam's minutes COULD go down - probably will go down. But if he develops more offensively, he may just hold that minutes reduction to a minimum.