Thanks all. That makes sense, and was kinda what I was thinking would be the case. Just wanted to make sure I wasn't being too cautious about it.
It's really frustrating not to even be able to get as far as a query, but I guess we should all be used to some degree of frustration by now.
Why would that frustrate you, really? It's not that Agent X is the only agent on the market. Just move on and find someone else who represents writers/books in the genre you're targeting, and you'll be fine.
Back in the day when I was still a staff writer, quite a few publications I applied to turned me down immediately because I don't have a college degree. Those editors, however, who looked past the missing degree and instead zoomed in on my published clips invited me to interviews, and not once did I not get the position offered after I made it as far as the interview. I could have been frustrated about those publications/editors who couldn't even be bothered to look at what I
can do and who were solely concerned with what I chose
not to do, instead I decided to consider that their loss, especially since I evolved into a leading writer in a couple of fields, award-winning'n'all, pretty quickly. So it actually turned out to
be their loss of sorts, quite literally. Lesson learned: If they feel that they are - for whatever reason - above even looking at what I can do, I most certainly don't want to waste my time with them and for them. They are simply not worth it. There are, however, others who are, and those are the ones I would (and do) focus on.
If you adjust your attitude towards such agents accordingly, any feeling even remotely resembling frustration will automatically disappear. Don't let frustration hinder you; let such an agent's stand-off-ish policies fuel your drive to find someone even better and more suitable instead. Good luck to you!