I guess I disagree with that statement, it is not all heroic. Is it mostly heroic, probably, but I wouldn't say all of it.
Now, I will say I too miss the more grounded style (3e and 4e art were the worse offenders of the crazy heroic style IMO) to some extent, but I really appreciate variety and I feel 5e and in particularly 5e24 is providing that more than any era of WotC art. It is not the wild west of TSR era art, but I am not sure I want that (I think the 2e PHB is some of the worst PHB art of all time).