Sideloading no, better revenue model yes
If Epic manages to break Apple's ability to protect users (because they DO mostly do a ood job keeping crap out), than Epic has broken one of the means by which you can keep especially the dumber ones at least safe to a degree. It is exactly because of Apple's control that it's safe - but that is really not the issue at hand, that's just used for leverage because if you break that, you break a lot of what Apple has worked on over the last few years. In other words, the real agenda would be harming Apple's privacy protections.
The visible debate is really about money. If Apple can lower its tariffs (which others have already done), that's one way, but the real problem is that Epic doesn't want to hand off 30% of its revenue, and blames Apple for asking for it, conveniently foregoing the fact that they would not have the remaining 70% if it wasn't for Apple creating that eco system in the first place (which, by the way, the Android store is simply a later copy of, just worse in terms of protecting users so Google's percentage actually delivers substantially less added value).
Do I think 30% is a bit much? Yes, but so far, everyone asked it and somehow that worked. If you want to find a real rip off, try selling a book through Amazon - and that too, has been a long established practice.
Personally I think Apple should have engaged a bit more before both sides opened up a costly can of lawyers and took it to court. I can't see a good outcome here now, other than for the lawyers. I do not think it will add value for users, and if Epic somehow damages the control Apple has it has destroyed one of the last places you can send a user to without too much worries that they'll screw things up beyond recovery. No, Apple's App Store isn't 100% safe (especially not in the gaming section where plenty of app developers are after the kids), but from a safety perspective it beats the Android one hands down.
Unless, as I said, the real agenda is removing those pesky controls so the smear of three letter agencies in the US finally get access..