I highly doubt that every blade of grass is interactive. What BotW does looks like a displacement map with simple spherical bounds ... (the blades of grass being bent further behind Link is not very plausible and not even Nvidia's state of the art solution simulates "every" individual blade, BotW makes a lot more simplifications for grass deformation than you think)
MHW may not feature combustible destruction as seen like the Far Cry series but it has far more destructible environments and that more than makes up for it. Furthermore the level design in MHW feels more populated and alive compared to BotW but there's other details to enhance the environment such as smaller roaming critters throughout the map ... (monsters intentionally targeting each other is also a part of the AI's new behaviour too, it's these small things that add up to create a detailed and highly interactive experience in MHW that sets it apart from last generation games)
Even if what you said was true there's still the issue of the Switch staying graphically accurate to the original art ... (I don't think the Switch would be able to render many of the same beautiful vistas even with graphical cut backs)
MH enemies have intentionally targeted and fought each other for a long time. Coaxing them into fighting each other is a common strategy. That's not new. The only thing new is how often they do it.
Enemies also fight each other in BotW.
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