So, what's wrong with that kind of repair? I mean, the glue gets polymerised all over the area & the gaps it fills, no liquid can get thru.
The false water resistance is due to adhesive under display frame, earpiece, speaker/mike & sim-tray. Back glass never spills, unless it's shattered all around.
BTW, from my friend's experience in iphones repair, they've seen water damaged devices in otherwise new condition, like 1-2 weeks from purchase date (by activation date). Just because of Chinese workers simply forget to remove adhesive layer protective film around an earpiece, so the adhesive won't adhere. Needless to say, apple rejected to service those phones.