I was told by "a guy" that would know that Matt did buy Tiamat, but this guy was also rather odd with the information so...
Watching the MtG group operate is really something to behold. I don't know how much of it is speculative buying or, as I said above, nostalgia adjacent. I have 0 MtG pieces, am tempted by some but of course given my general tastes it is not the mainstream artist I find appealing (I would buy a Scott Kirschner piece if I could). The new stuff looks very flat and homogenous to me. I cannot discern artistic styles (except Donato). All the squirrel stuff just makes my scratch my head. I do know if I was an artist given a hot assignment I would certainly need to utilize an abundance of sketches and prelims to, you know, get the piece right (not to sell later, I swear).
That I paid much less for a classic 80s Ian Miller Games Workshop piece than a brand new MtG piece is also interesting.
Finally, I will say that MtG doing what its doing certainly sets price baselines throughout the fantasy genre. I have "overspent" on classic 80s fantasy art because, in reference to what similar buys in the new MtG realm, it all feels like a bargain.