Chaosmancer
Legend
Why on earth would monsters and foes stop having expectations? It is a natural and logical thing that intelligent creatures will make judgments made on the history and habits of the known races. Halflings are poor fighters, dwarves are bad wizards, elves... are elves and bards should all be staked through the heart ( but that is an other topic.)
This is what fixed ASI make for the players. A chance to metagame by playing the unexpected. Because at some point, the stereotypes are reinforced by the racial ASI and thus monsters and foes will have the same expectations.
You jest with my RP, but I do RP monsters and foes with their basic interpretations and alignments. And I sometimes surprise my players with.... an unexpected build for a monsters. "But (insert any foe) are not supposed to that!" is a sentence I often hear at my table. Because even if the vast majority of my villainous creatures are in the MM, I can work with my players expectations too. This is exactly what role playing is about.
Now with generic RPG where you build what you want, there are no particular expectations as the lore does not provide any. GURPS, to mention one, is a really good system but it is generic and every race can do anything equally well. So intelligent foes will behave differently with no special expectations because there aren't any to begin with. D&D I unique in that it's lore is (so far) supported by mechanical rules (racial ASI and powers/skills) that many other non D$D related RPGs do not have.
Instead of taking one aspect of a game or post, try to look at it in its totality. This will let you understand a lot more my point of view as I do not focus only on one part of the game but to all its related part. Racial lore is as much important as the mechanical aspects of it that reinforced each other. Thus, this creates expectations and assumptions in both players and monsters about what the general adventurer of each race can usually do.
A very long post to say a whole lot of not much.
Every Mountain Dwarf can wear armor and use a hammer. As a commoner, that would mean they are swinging a normal blow that has a +1 to hit and deals 1d8+1 damage.
So your monster sees a dwarf in armor and with a hammer, then they run forward, and swing that hammer so it crashes in to the monsters friend with a boom of thunder that cracks their spine and sends them lifeless into the dirt. They made that attack with a +7 and dealt 2d8+4 damage. That is massively better than any dwarf they have ever seen before. Why don't they react with shock and surprise? Dwarves can't do this, dwarves attack at +1 and a deal 1d8+1 damage.
Or maybe they've seen an adventuring dwarf before, so they could tell me exactly what class that dwarf is and what abilities they were using and how they got them?
Halflings are poor fighters? No. They are poor strength fighters, they make for excellent dex fighters. Even in the realms of optimization.
Dwarves are bad wizards? Maybe in the realms of optimization, but in a world where the commoner wizard would have a 12 INT, any PC wizard is far superior.
Again, what you are describing is basically that the monsters are metagaming, because they know if you picked an atypical build and react with shock that you are capable of something most of your race isn't... and since most of your race isn't a PC class, that's just about everything you do.