They're totally defense seems to be sufficient without Tim and with West in the starting lineup. I know the narrative is that the defense fell off without Duncan, but people overlook that the pace increased without him as well, which contributed as much to their higher PPG allowed. And the team played two great offenses without Tim, and that obviously skews the stats even more. Obviously Tim is a great defender and important player, but the team got by without him.
The Spurs didn't have an elite starting unit offensively with Tim and LMA there together. They only really started making their way up the ladder when Tim was out and LMA got into a rhythm. He went for 22ppg on 58 percent shooting without Tim and has dropped to 14.7ppg in 44 percent shooting since Tim came back. It's shocking how much better Aldridge is as the starting center.
Of the first three guys you listed, Hibbert is the only established starter. Cole is a low-minute guy who's foul-to-block ratio is horrible, and Plumlee can't even get a rotation spot recently. Truth be told, they aren't bad ideas for pickups. But no way do I consider them starters or think they make more sense to put next to LMA than a higher-end PF. Grant's about to be boxed out for minutes with Noel, Embiid, Okafor, Saric, Covington and almost certainly one of Simmons or Ingram in the front court. Philly wouldn't cut him or anything, but I do think the Spurs could get him for a pick.
I feel like you're getting it twisted. My point isn't that Horford is a center who can't be anything else. It's that he's managed to succeed as a center his whole career despite being a worse version of LMA. Sure, people have complained that he's a natural four, but that hasn't stopped the team from playing him at the five, Horford from excelling there, or the team being good despite the lack of a five next to him. In a similar way, the Spurs have tried to put the best big they could next to Duncan. It was a stiff back when they needed guys to guard Shaq, KG and the other elite bigs. It was a screener or popper when the Spurs moved to a PnR-centric offense. It was an agile big when Tim just couldn't take the pounding of being a defensive center for an extended period of time. Now, it's a big-bodied big who can shoot and roll now that the Spurs have the money to check off that many boxes. I don't think the team cared if he was a natural four or five outside of lineup designations. And I don't think they care about it in terms of LMA either.
This is really the key point. YOU'RE talking about maintaining the status quo. I'm not. I'm very much not. You don't get a scrub to be Duncan. You create a different paradigm where the five new guys can all play the best. Same thing is true with the bench next year if/when Manu leaves. You don't pretend like Anderson is Manu and leave it there. You're not going to be able to replicate that beautiful game play just by adding another passing wing. You do something else, and maybe some of the current guys there won't fit that new thing. The important thing is for the Spurs to get the best guy they can this summer and figure out how to make it all work after.