This is a tired argument. No the older console isn't going to hold back a title any more than a low end PC held back how gears of war 5 looked and played ( Which it didn't ). Games that scale is nothing new. Single games could have different features, render paths, you name it. Xbox is NOT tied to PC in anyway. I don't know where you get that failed narrative from.
When MS shows first party games ( and we have already seen glipses of a few) that look as good or better then anything you have seen coming, then i'm sure you will change the argument back to "Xbox has no exclusives", or "MS should sell the xbox division", or the best one ever - "It only sells in america and england anyway".
The things is a game as you describe which always scale doesn't matter the hardware is not about if is impossible, the word should is unrealistic.
The games even in PC establish a minim spectrum when the game is playable and recommended when is the dev think is the optimal experience, yes
most games are designed for be played in PC to 60, if you increment the spec of your PC you only will increment the framerate until the engine is capable
but in the end a game experience is the same if you play in 60,120,240 Hz, I mean the game experience not the fluidity of the game.
But that doesn't mean is realistic from a studio use as minum the GT 210 and the recommended the RTX 2080, because the quantity of work in order achieve this will
require a stupid number of time and money which you will not find in this world. That is why the development establish a goal, also usually for this reason the biggest
steps in graphics and some mechanics happens in the jump of generation, basically as being the main market for most the studios its threshold moves with the consoles
so now the can focus in do other things.
You usually see example of game which looks better than before but are not so impressive because those games are intergenerational, so in this situations they only have a couple
of options:
1-Dev the game as always and only use the high settings of PC in the new console (Assassin's Creed Valhalla) this is the most common
2-Make two versions of the same games and mechanics (Titanfall) this is weird as is expensive
3.-Something similar as the first but also they need to remove mechanics because in order to make it work they needs something of a most recent hardware has (Nemesis system of Shadow of Mordor )
4.-Base your game in the new console and then cut probably with not enough time to optimize for the weaker console (Forza Horizon 2) even this games can have worse graphics than its prequel
Note: you should avoid the use of strawman fallacy as in your last paragraph.