Firstly i'd like to address zaifys concern of varied fleets. A single or 2 destroyers does not equal fleet varietion. Dread spam is not entirely negative either. Testing has shown that a good cruiser can take on a Dreadnouht. Its more a matter of different navies adopting different ships through testing then forcing a single destroyer which represents "variation" somehow.

It think a solution to this would be for mini naval seiges where only destroyers/escorts can be used. Perhaps a convoy mission where one team has to transport, the other sink or a mini region where dreadnoughts cannot be piloted. This however is a different suggestion entirely. Variation can only come if people are willing to experiment, and i believe calling an additional destroyer 'varied' is a lazy excuse imo for the fact some ships have 0 use value. I still believe destroyers and cruisers have uniqie abilities against dreads.

Further what role should a submarine have? I believe one of strategic importance rather than battle importance. Subs should be slow like irl and have to be at the right placr in the right time to sink a dread. They should not be able to chase surface ships. This means that pilots no longer can attempt to swarm a dread, it makes them less of a threat and effectively would kill subs current state of killing ships that cant kill it, as such a practice is unfun and unfair. Subs should be a secondary threat, not the biggest worry on surface ships minds. This also mirrors the actuality of submarine warfare.

Lastly I reccomend you check previous suggestion to understand where this comes from.

Ruleblocks suggestions are also full of good ideas.