Here's the thing - there are only two lords of Gondolin who are 'important' characters - Glorfindel and Ecthelion. Both of these characters will need to be introduced to the audience in a meaningful way. So, what we are really looking for is a way to introduce Ecthelion.
We can tell Rog's story (with Rog renamed), and have a minor character in Gondolin who will die fighting outside the walls. That's fine.
But it doesn't solve the problem of how we introduce Glorfindel and Ecthelion properly. We do want Ecthelion to be an epic fighter. So, while the 'capture-torture-and-release' trope could make him a second coming of Eonwë, it's only one way to get there. Any other suggestions on how to introduce him? Those can probably go in the general discussion for Season 4.
For the purposes of casting, Ecthelion should be a strong fighter (he's going to take out Gothmog, after all), and he should probably be dark-haired to contrast with Glorfindel's blond. For elves, we tend to like tall actors (so, 6'), and between the ages of 25-40. Good singing voice? (I only put a question mark on that because if we don't have a scene planned where he sings, we don't really need that. So, as Season 4 unfolds, we'll know more.)