Note that I am talking about these Airalo, Nomad, etc eSIMs sold online, not eSIMs sold directly by the carrier themselves (the latter would generally be as good as the carrier's own prepaid offering).
>I've tried a few of these and can rarely pull more than a few megabits per second (in a location where a carrier's own SIM pulls 150+).
That seems.. fine? If you're traveling and your use case is checking google maps, or logging into airbnb to pull up your booking, you don't need 150 Mb/s of speed and low latency. The only case where it might be dodgy is if you're doing voip calls or watching streaming videos, but why are you doing those things on vacation? Sure, it'd be nice to have a local sim with low latency and high speeds, that's often much more expensive than esims and/or comes with more hassle (eg. KYC or having to pick up the sim in-person).
I've used them quite a lot around Europe and once or twice in Africa (and even locally, when I didn't have an unlimited data plan and used all of my allotted data by my carrier and it was easier to just buy an eSIM), and my experience has always been pretty good.