Yes, I like that feature - that most (maybe all) of the companions that go only to one sub-group of pirates (those whose parents were squid snacks, those who like to swing around on ropes and poison people, etc.) can be purchased by others. Or, indeed, doubled down on (my swashbuckler has Sarah and Lucy - they have a running competition to see who can skewer more opponents; Sarah has "flanking" and is pretty fair ahead of Lucy, who took "Bladestorm" instead).
I also like that the two versions, while functionally identical (assuming you pick the same talents/feats for them) are fairly easy to distinguish - Sarah and Lucy have different colored fur and dress differently.
Louis I don't regret at all once I trained him to 50 and got his last promotion. He fits well with musketeers since you can lay up to three sets of mortar shells which are quite devastating. He was a pain earlier on with he promotion quests but is solid and quite tanky. Sarah I think is the best all around companion a class can get especially since coupled with lucy and the right passives you can chew through anything. I think in the end though it should stay the same. The option to buy things in the crown shop with gold should be expanded to include companions which would solve your problem.