The pool of talent is no greater now than it was then.
I would argue it is significantly larger now.
Not only is the population a lot higher, but the basic barrier to entry to getting art out there and seen by people is significantly lower, and women and minorities have fewer barriers to entry now.
There's a reason the same few artists were used over and over by TSR, and it wasn't that they were the only good artists or something, it was that they were artists who TSR's art directors were actually aware of and in contact with, and in the 1980s and 1990s that meant the real-terms talent pool was, far, far smaller than it is now.
Plus it's far easier to commission art from people in different countries and continents (and WotC has done so before), so I don't think it's possible to even argue that the talent pool isn't larger.
The one countervailing factor is that videogames tend to absorb a huge number of artists who might otherwise have worked on TTRPG art, particularly as concept artists. But I suspect that's not extreme enough of a factor to make the pool the same size or smaller.
That said, what I don't know is whether art is relatively cheaper or relatively more expensive to commission these days. But whether WotC are willing to pay is different to the size of the talent pool.
EDIT - Frankly one need look no further than MtG to see how massive the talent pool is now.
That's the trend with the 20245e
It's been accusation levelled at certainly 2E, 3E, 4E, and 5E as well so not a particularly damning one.