Agree. Also, given TL's injury history, they need a high quality backup C, ie what Theis was supposed to be in theory.I don't think you need a long term Horford replacement. I think you have gone ultra big in part because of Al's rare combination of skills
Long term the answer is probably more Tatum at 4 and getting 2 of Brogdon/Smart/White on the floor at almost all times
I don't think Collins is a C, and playing Horford fewer minutes lets you sort of make him that backup with higher probability of health. Still would like to add someone there.