if we are bringing "real life lore" into this, in reality submarines wouldn't be anywhere near the surface to take any damage from someone shooting the surface of water 100+ meters above them at a very horizontal angle at that (making most of energy wasted horizontally and getting deflected off it, explosive (summit) or not), square law also works for compression waves if you want to push the "but it's an explosive", even real bombs exploding at surface of water would just be sonar noise to submarines at their appropriate combat depth
and the "it takes micro" excuse doesn't work either, this is an issue caused by limits of simulation and is only currently "balancing" the units around this micro because there is no easy way to fix it (such as would be to lower submarine depth, which afaik is impossible to do because engine, and obviously doesn't work on maps with shallow seas but that can be considered a map specific gameplay)
to steal reuse an argument I already did in the atlantis thread, if submarines should be possible to get hit by surface weapons, then surface weapons should automatically target them as well, especially since how easy it is to do so already, micro or not (groundifre above them) before you say something "why can't mobile arty target air", maybe seeing battleships automatically targeting submarines with surface cannons would convince you how ridiculous it is that this can happen at all even if needing micro
if we could just make submarines go lower to avoid this problem then I think the development/balance team would have already done so
I thought about maybe having submarines "walk" on bottom of ocean instead, like ACUs and wagners do but it would look weird even if possible as they should move like ships, not tanks/walkers, and would probably clip into the ground