Nah. Just my opinion, but I don't think adding another defense (in this case a legendary pirate) will have much effect on the state of (in) accurate replays. at least I hope not.
For attacking, if its anything like it had been, they take 1 slot, cost a large amount of gold, and there's a limit of 1.
I think they will be specific to defeat certain types of bases. I think they will tip the scale against current base designs. Since you will have to pick legendary before attacking you will be targeting a base they will thrive in. So new lay outs will have to be created. Am thinking shark trap will be useful against some of them. Dont even know what hp are yet some of them might be fragile but useful if deployed correctly.