That assumes that the apps you need/want are still available from the App Store. If a company/developer thinks they can monetise their app in ways that would fall foul of the Store rules, they might try making it side load exclusive.
The attraction of the App Store for many is a) one shopfront, b) one secure payment method, c) curation, d) some sort of initial/ongoing screening for malware and e) remote deletion for a discovered bad actor. A particular software package is unlikely to become cheaper after leaving the Store, as hosting, payment processing, etc. are not free to obtain and the object is to make as much money as possible, so how does the consumer actually benefit?
That said, I think it will probably turn out to be a bit of a nothingburger, given the stats from the Android side. I am sure that side loading on iOS will default off and require acceptance of some pretty frightening (to non-techies) possibilities, so the overwhelming majority will likely not bother. For developers, the loss of customers who would have discovered their product in the App Store will have to be set against any possible savings from the 30%, assuming they can actually do it significantly cheaper anyway.