Submarines have their use but suffer from game changing and sea/water maps generally being disliked.
Before there were 2 types of submarines instead of 1, while it doesn't seem much it's double the current amount and allowed some role specialization between the 2 submarines.
Current submarine was the generic sub not much different now compared to before, and the old removed sniper submarine that turned water maps into equivalents of Pillager/Impaler vs Stinger.
That combined with removed option/ability of submarines to change their depth level, like air bombers can choose between low and high altitude flying.
While it doesn't seem like much it allowed subs to hide deep under water away from nearly every surface-to-surface weaponry that didn't have obscene AoE and if water was deep enough even dodge Raven bombs.
Or if the water was too shallow you could make the submarines surface so they can move through but suffered from being visible target to surface units, but it could also cloak if under an area cloak since it's not submersed in water anymore.
There was also the old/rare multi-weapon capability of ships, Envoy for example had depth charges to deal with subs(the little empty spot in the rear of Envoy), like Siren has the sonic weapon and the long range missile.
Maybe if there is enough motivation the old heavy sniper submarine could make a return, either in original form/role or a new role(Ships already have Envoy for artillery and long range sniping so old version is redundant).
