You are quite right in all of that. I misspoke in saying pdf format causes issues, it's Adobe that causes issues. Like you, I found that I have had to resort to adobe acrobat software only in dealing with the IRCC and I detest doing so.I'm also on apple and having to use the Adobe software is a PItA. But apart from that - which was annoying but not much more than that - it was perfectly fine. Caveat that this was before the fully-online and I suspect now it matters even less (they all suck due to IRCC's bad websites).
I'd only say though that this is NOT because apple does less well with PDF - in almost every respect Apple uses pdf 'natively', just that IRCC is dependent upon Adobe and Adobe likes to do weird proprietary stuff, whereas Apple in this area adheres to the published, open standards. (And because apple users have typically zero need for extra pdf solutions, adobe doesn't make their software a high priorty on apple computers.
This can be seen fairly easy by one thing: I've been basically an apple-primarily person for more years than I care to admit, and I've never had to resort to the adobe acrobat software for ANYTHING else except IRCC. To be fair my previous corporate employer had all-windows and I might not have noticed if anything required adobe, because acrobat was installed all over.