sounds like its working for you, so i'm glad. you're about what i'd consider a big team / codebase. i can't recommend TS to people trying to create product from nothing. if your startup is doing well, you can hire someone to annotate your code w/ types later ;)
they mention a time tax of 262 seconds median for TS annotations for their set of 400 bugs. almost 4.5 minutes. so idk, there seems to be some math missing in this paper about the actual trade offs. so maybe you get a 15% improvement in "detectable" bugs found, at a 13.3% time cost (60 minutes /4.5 minutes) per hour of work. worth it...? are your devs expensive? more expensive than QA.
i'm tired of devs that claim that TS and GraphQL are "self-documenting" and don't need to write any documentation. it doesn't fill in the common gaps, it's just an excuse to not have to think about or talk to users.
nope - the loss in velocity is not worth using it unless you're a massive team. TS is for Java programmers who are mad at Javascript for existing and don't know how it works well enough to grok overloading etc. plus you get a lot of the benefits of TS in an IDE like VSCode without actually having to use types at all. if you're a javascript native, typescript is constricting and eliminates one of the best parts of javascript - no types!!