The only other rotation players who could possibly play power forward are Jaylen Brown, Grant Williams and Semi Ojelele.
We are asking Theis to adapt to a position he has never played in the NBA. It's a big change to go from center, where he is quicker than almost everyone he plays, to power forward, where lots of guys are quicker than him. Give him 20 games before giving up on him.
There may be an opportunity at the trade deadline to get a starting power forward, but that is the primary need this team has. We cannot let Theis go for any other value proposition. If you don't like what Theis is bringing to the position, I doubt you will consider Grant Williams the solution, unless he somehow makes a major leap, and that would only work against smaller lineups. We need him.