I used to work on Stripe Checkout and your interpretation sounds like what my understanding of the situation was at the time I was there, yes. Basically Stripe provides everything, isolates the code as you said, and for 99% of merchants you just hit a button and get on with your day. I think for the other 1%, from reading the docs you linked, it sounds like for particularly large businesses it might cause a couple days of work, but orders of magnitude less than rolling it yourself?
