I wonder if that's an American thing, every time I tried to do a chargeback here in the UK on a credit card my bank said they have to investigate first, give the seller an opportunity to respond, and only if that fails they will refund me after 60 days. While everything I see online suggests that Americans can pretty much do an at-will chargeback for any reason with instantaneous effect?

Yeah, pretty much.

I used to work for an online retailer that sold high-ticket machinery parts. It wasn’t uncommon for us to face chargebacks on orders worth around $20,000. Eventually, we had to get chargeback insurance, because the only way to contest a chargeback was through a mercantile court.