Well, I'm not sure too many thought of Davis, Britton or even Manny as top end talent early on. That said this has been a pretty devastating year development wise.
Manny was extremely highly rated. #3 pick in 2010 draft. Top-20 overall prospect heading into 2011 by both BA and BP. Climbed to top-10 heading into 2012, then made his debut that August in his age 19 season and took off basically right away.
Davis and Britton had top-75 prospect pedigrees at a time (higher for Britton), but both struggled immensely in early MLB chances and were basically dumped. Certainly fair to say nobody thought they'd be star level players at the time they got to Baltimore after failing in Texas in Davis' case or moved to the bullpen after failing as a starter in Britton's case.
I'd say we have a couple guys who compare to what Davis and Britton were rated when they were in the minors (Sisco, Hays, Diaz, Mountcastle, Hall). So even if they come up and fail initially, it's still possible they end up being major contributors or even stars. We don't have any stud prospects like Manny was, or Adam Jones and Matt Wieters before him. Stud prospects don't always make it though, as Brian Matusz can attest to.