Surely if a rejection was for a reason that a couple weeks of study could "fix," it wasn't worth a rejection, right? Are hirers out there really being THAT picky?
I'm going through resumes right now and rejecting people if I think they need a year or more experience under their belt than what they're presenting. If it's because they know react and not vue, that's not reject worthy at all...
I don't remember 99.9% of what recruiters have said to me, but I do remember the two companies (Hulu and LinkedIn) that made me feel like crap and jerked me around. It was 2 years ago and I'm sure most of the people who were a part of that are gone, but I still kind of have that grudge.
Where I work is an agency, so essentially a collection of already experienced designers, engineers, etc that need to be building quality products pretty much day 1. Any of our time we aren't billing to clients is just coming out of our cut.
It's a somewhat ruthless calculation, but we already skim billed time to do things like give ourselves 20% freetime to work on libre projects, train ourselves on new tech, etc. Some of us use that 20% to mentor bootcamp grads (me) which is the kind of help I want to give to green engineers - I'm a selfish boi and don't wanna lump a billable hour cut on top of that. We absolutely don't have time to be pulling someone in that needs 3 more years before they're engineering at the level we need.
Some companies do actually hire people fresh out of college/coding boot camp, and for those people, some feedback and a few weeks studying might make a world of difference.