This seems like a well articulated case that you're making, though I'd like to argue from the opposite perspective for a bit.
> If you do not acknowledge this is the case, then DEI efforts can seem very unfair.
This is a non-trivial objection. I struggle to think of many acceptable scenarios in which we have to choose between acknowledging something which we don't believe as true, or living in an unfair system.
Likewise, I don't know of any people personally who object to DEI efforts to make fields more appealing to a wider audience, or bringing in more diverse perspectives, or even critiquing existing processes.
The main objection that I see is against the policies which are enacted in pursuit of that goal. For instance, saying "our engineering team is largely Asian, we might be missing other perspectives" is a good call-out, and I can think of nobody who'd oppose calling that out. Enacting a policy that said "for the next engineer in this team, let's make sure we hire a non-Asian employee", that is the source of a lot of the umbrage with DEI efforts.
In my experience, opponents largely agree with the goals (more diverse viewpoints), but disagree with the methods (pandering in the best case, and preferential treatment by group in the worst case.)
You are correct that there is no inherent cost to learning about and bringing in different perspectives. There is a cost of the efforts to bring in those perspectives if they mean that I lose a job that I would otherwise have gained.
Moreover, an even bigger concern is that these decisions aren't being made based on perspective, but only on immutable identity (e.g. race, ethnicity, gender). In these cases, the cost is even greater, since one can't address the situation by bringing in more perspectives; if the company says "we need more non-Asian employees", it is a really big cost (and one you can't avoid) if you happen to be Asian, regardless of how many heterodox opinions you might otherwise bring.
Nobody I know opposes thegoals of DEI, but it's not hard to see how policies enacted which disadvantage people based on immutable characteristics might be reasonably considered unfair.