Originally posted by Shad1902:

you answered your own question.

sub spam is not worth it, because subs are not good to control sea zones...

meaning, subs should now be used for what they were designed for: convoy raiding

Seems like it. I hoped there would be a "if you do it that way, it still works", but i guess not.

nah, not really.

As for IC costs, roach-DD's are pretty cheap if you're concerned about your economy.
granted, more expensive than roach-SS's...

Submarines works agains countries like UK if you can prevent it to get oil and any other recourses... Afthey they don´t have oil... they become ripe to be conguered. But agaist other countries... not so much...

The current meta is glass cannon light cruisers stacked with as much light attack as possible to shred enemy screens, supported by torpedo destroyers in the back to finish off the capital ships once the screens are gone.

Cheap fleets like this can absolutely devastate even major nations navies while still being very affordable.
The only real weakness is air superiority and naval bombers. If you sail too close to a coastline without air cover, you might end up rebuilding the entire fleet from scratch afterward.

Sub spam is still very powerful, just not alone.

As above, you need some form of surface ship. Spammable CLs or DDs are always nice. The AI still seems to be terrible at managing its navy, both in terms of production and actual deployment.
With the changes to research it is easier than ever to outpace the AI in naval quality. Combined with the AI’s inability to manage good fleets, submarines can still wreck when set to always engage. It all depends on if you want to do naval invasions or not, tbh.

Naval pressence is naval pressence. Surface or sub. Putting subs on patrol, builds up naval dominance just the same.
Than have another taskforce of subs convoy raiding the same area, for lowering enemy dominance. Naval bombers will also help keeping enemies away, or force repairs