Had Isaac Newton not come up with the laws of gravity, certainly someone else would have in under fifty years.
Had James Watt not built the first modern steam engine, certainly someone else would have in under thirty years.
Had Edwin Hubble not observed that there are other galaxies out there, and that they appear to be moving away from us, certainly someone else would have in under thirty years.
And yet, we still celebrate each of them for their achievements. Why should Ada Lovelace be any different?
Also, why does every leader have to be the very best to be included? Are we limited to only the best military commander, only the best strategist, only the best philosopher? We don't necessarily have the "best" Roman emperor in the game, but they still obviously picked someone notable with accomplishments.
I mean, sure, obviously you can argue whether it makes sense to include a mathematician/computer scientist as a leader. Obviously there can be some debate there. And yeah, once you concede having one in, you could argue that maybe they could have picked Einstein, Euler, Euclid, Babbage, Turing, etc... as another option. But just like for civs, they don't always pick the top option, sometimes it's great to find an alternate option that still had a sizeable contribution, someone who people don't know much about, and who makes for an interesting choice. Would the game sell more copies if they picked Einstein as the playable leader? Probably. But if you're going to let scientists in the door as a leader choice, I have no problem at all going with someone who is A. Not as well known and B. who make enough of a contribution that they probably should be more well known.