In short - yes, it's fine, particularly under those circumstances. We adopted via a Voluntary Agency and our family finder said ideally no more than four concurrent enquiries. But it's going to take you a million years to find a match if you pursue them one at a time in series, instead of at least somewhat in parallel, for exactly the reason you've discovered - so many of the people on the other side fielding enquiries are incredibly unresponsive.
I have to say that I'm not sure we would've wanted four open enquiries at one time and there's some judgement involved obviously as it depends what stage the enquiries are at. In your situation I would absolutely be still looking at every profile, every day on LinkMaker and making enquiries about any that felt potentially right. So yes - go ahead and enquire.
That said, the previous advice about checking which LA it is definitely stands, and in general it's best to discuss this with your family finding social worker.
Best of luck finding a match!
We had enquired about Child 1 and had a similar experience when we found Child 2. Child 2's social worker got back to us very fast and then followed a slightly painful experience of trying to extract sensible/ good quality information from them whilst they pushed the pace as much as possible (it's a long story and not for this thread, but they had their reasons due to what was going on at the time unknown to us, but it came across incredibly badly to us and as if they were trying to hide something - and our social worker agreed!)
Anyway long story short, as we learned more about Child 2 gradually we continued to ask our social worker to push for a response on Child 1 and we even asked for information about Child 3. But along the way Child 1 social worker finally got back to us with a no, and then we stopped chasing for info on Child 3 as Child 2 was definitely going somewhere (and we were linked, then matched, then Child 2 came home to us and now we have our AO!) We always felt really strange about Child 2, the one we were matched with, being the first child on whom we received any proper info (Child 3's info came to us later). It felt really odd that we only ever 'got to know' one child and 'went for it'. But at this point I'd say it was definitely the right thing.
Short story: Family finding is stressful and LinkMaker is awful, and the 'system' in its broadest sense is very overstretched. Don't hang back at this point, go for it! (albeit you're right to think about how things 'look' even now. One of the greatest things about receiving our AO was finally, finally. I no longer care what [insert long list of professionals] think about our motivations!
Good luck!