A core part of the EU law is that the repair should not require detailed technical expertise or uncommon tools. The current iPhone 13 design is not even remotely close to that. It requires a pentalobe screwdriver, a y000 screwdriver, picks which can only be inserted 3mm, a special clamp, a hairdryer to melt glue, and finally isopropyl alcohol.
The iFixit guide consists of 30 steps, with several warnings about accidentally causing significant damage. That is quite a bit beyond the intended "open battery cover using philips screwdriver" type of repair.
If the back was screwed on vs clipped on (allowed with new laws), it could have easily been ip68 rated.
Apparently a similar hole into the enclosure for the Lightning port was impervious to water in ways other holes weren't. The RDF kept the water out.
I've owned multiple waterproof phones with a simple o-ring gasket around the battery door. Low-tech I know.
[1] iPhone 14 earns a 7/10 score on iFixit thanks to new back assembly
https://www.gsmarena.com/iphone_14_earns_a_7_10_score_on_ifi...