They just said that to make people feel better. My Samsung A8 2018 with jack port is IP68/IP67.
Fewer seals, fewer seal failures. (Salt water can be fun on the metal contacts, too.) I expect Apple to go induction-only charging at some point, for similar reasons.
Waterproofing is possible right now and works for almost all normal use cases. No need to remove features.
What Apple is doing is definitely not for waterproofing.