We don’t know that Starfleet has taken a step back from no warships in the early 25th century. Defiant was a response to the Borg threat and Prometheus was an experimental ship during the time of the Dominion War. The last in universe appearance (not counting possible futures) of both was what 2378 ?(VOY Endgame) & we are now in 2401 ? They could all be decommissioned. For Inquiry all we know is that they’re the toughest, fastest, most powerful ship… That doesn’t necessarily make them warships, could be multi mission explorers like the Galaxy. Taking lessons learned from the war and encompassing them in future design strategies.
As far as Defiant being in the museum, remembrance doesn’t equate to celebration.
Well I always remember those words of Will Riker:
Right now I'm on the bridge of the toughest, fastest, most powerful ship Starfleet ever put into service. And I got a fleet of them at my back.
He's talking about Inquiry class. So it seems that's a warship some kind.
