Not taking either side here - but surely a lot of cosmological phenomena couldn't be testable/verifiable at the time they were theorized either?

(thinking of black holes for example - they were theorized way before we had observations. And presumably a lot of particle physics can similarly be theorized before we built the technology to experimentally verify them)

Sometimes theories need engineering to catch up to become testable.

Well, we can test it, but you'll need to give me a ton of money in order for me to test it.