[nfc]

Couldn't we run experiments to discover whether they really have this role?

Like for example choosing an island with mosquitoes (and far enough from other lands as to not be rapidly repopulated) eliminating them there and seeing what the effect is in the ecosystem?

I wonder if something like this has ever been tried.

[interestica]

I think they're deploying these (https://www.oxitec.com/en/our-technology) in the Florida Keys (https://www.keysmosquitoproject.com/our-solution)