1) A capital without range advantage can't do anything against a much faster DE. As a DE I'd just attack from exactly max range retreating just a bit when I need to vent. 2 DEs could easily tag-team any capital that doesn't one-shot them with TLs.
A capital would still have more long-range firepower, since he has more big guns.
ON a another note, do you think the ship COUNT limit should be replaced by a total FP limit (for player). right now, because max fleet size is determined by a number of ships, everyone endgame fleet is all capitals to make max use of it. But if you run that into a FP limit, then you could have a larger flee of smaller ships.
But capitals don't, as a rule, have bigger guns, because lower ship classes also have large mounts. And the range difference between medium and small isn't that big. And a lot of the firepower of capitals is in other mounts than just their larges. And there are long range mid sized guns - HVD/mauler come to mind. Not to mention beam spam at 1000 range, though thats less of an issue as its soft flux.
There would need to be a complete rework of the weapon ranges and mount composition of ships to compensate. There would need to be lots more weapons and mount types, because there would need to be a variety of weapons on cruisers/capitals for it not to be boring, but due to the range/speed restrictions they wouldn't be available on smaller ships without severe balance problems. Would cruisers even get capital weapons? If so, then they are faster and longer ranged, not good.
Its a lot of work for marginal gain. We can use years of hard earned knowledge: slower speed --> longer ranged maintains balance.
As a case study, look at the Falcon. It has lower firepower than several destroyers combined with weak defenses for a cruiser, while costing 15 supplies/DP (and 3 fuel/ly). Its ordinance points are low while its hullmods are full cost, and its flux stats are nothing special. What it has however, is range and speed combined: even with all of the deficiencies I listed, the range + speed combo makes it a darn good ship against every class of enemy.
For the side note: Personally, I think the combat system fails to work when the battle is too crowded - ships get in each other's way, pathfind strangely, and just generally the AI derps out and fails to make good choices because its too crowded. While it is a bit 'gamey' to limit the ship numbers, because I feel that it makes for more exciting, better gameplay, I am a supporter. The only exception is that it also messes up the salvage opportunities for industry fleets - I think the new system fixes that? I hope?