@ MM: OOOH I have heard of that! That was listed in the history of copyleft! ...but I will admit to knowing little more than that ;p
@Barak: You will notice that the SoL enslaves Frigates, because I also liked the idea of navies full of captured ships. However, I seem to recall that many navies practiced this same strategy of capturing and utilizing enemy ships (Suffren (French) did this in India for certain). I think we can assume that most navies would understand as simple a concept as this.
Since it gives them a defensive warship (one designed mostly for escorts and blockades, but also limited cruising) it is a very valuable trait. My biggest gripe with the changes I have listed is that the Frigate is capable of duking it out with a ship of the line in actual combat... but since I consider bombardment to be the actual line combat... and since the Frigate lacks this... I think it makes up for it.
One change I would suggest (going to edit the original post for it) is to give the SoL Lethal Sea Bombard as yet another ability in order to make it extremely important.
I really did try and post stats that force roles similar to those of the actual ships. For instance, SoLs will only be useful when protected by smaller ships, but in fleets will dominate all that opposes them. Frigates will be more useful for escort missions and patrols, but not very effective at major combat in an offensive role (despite being essential for defense). Galleons are more multipurpose, with equal A&D and ok bombardment. They basically can do anything, but nothing well.
The British MoW (retaining its Galleon position in Rhye's upgrade tree) can do everything the Galleon can, but better. It can operate independently of frigates (VERY VALUABLE!) but is best utilized in conjunction with them. It seems that I have accidentally made frigates more valuable than they should be... but really, this is the only way to make them at all useful ;p
I do not think it will really be necessary to move ships from their current positions on the tech tree.