How far down the line is that canon defiant retrofit though?
Starfleet won't have a modern escort ship for all of that time.
That's definitely an additional issue to consider, although potentially one we can live with.
One factor on taking on the
Defiant project is we have to to either solve the issues with the ship being over-powered that Starfleet designers could not canonically (until Miles O'Brien came along), or produce a less powerful design. Now I think we're pretty smart cookies, so we may well be able to do it, and was players we can assume a degree of narrative agency which may make it possible for us to surpass the "default" performance. But all that being said, it may still be a difficult needle to thread.
The Peregines are still a weird SF decision. Those things had no business going against the Jem Hadar.
So this may be a bit of a hot take, and apologies for disagreeing with you, but I would actually personally say the exact opposite?
Far more so than the Defiant, which still ultimately replicates most of the canonical "starship" features like extremely high endurance and reliability, science labs, and shuttle bay, and so on, the
Peregrine class really does seem to be a "pure warship" designed to trade effectively with other ships. With a crew of exactly one, very limited amenities and endurance, and at a size not much greater than a runabout, it was still able to fit phasers and a rack of full-sized photon torpedoes, with runabouts for comparison only carrying miniature ones. Yes, they suffer high casualties, but World War II torpedo and dive bombers also suffered pretty eye-watering casualties. If a
Peregrine wing can destroy or cripple warships a hundred times their size and cost, then the calculus is worthwhile, and in their on-screen depictions they are shown doing so a few times.
There's actually an analysis of the
Peregrine class and how it plausibly fitted into wider Starfleet doctrine on the
Daystrom Institute subreddit which I really like. It also goes into some interesting speculation based on how different doctrinal choices regarding the design of their bigger ships, it seems plausible that only the Federation might be well-placed to operate smaller fighters of this type, because only the Starfleet invests in large multirole vessels with a lot of shuttle capacity. (This implies that the
Reliant class may also have a very successful second lease of life as escort carriers during the Dominion War).