We did mount our TV over our fireplace (gas), but built the fireplace and surrounding cabinetry very low. We always recline a bit so it's a better angle for us....either in a recliner, or leaning back in a chair with ottoman. Personally, I don't like the TV too low. This is just a personal preference. Because our mantle is quite deep, there is no issue with heat from the fireplace. We had the TV professionally mounted (not by the people from the store where we purchased the TV) and they said the heat was not an issue in our room. It's been there for several years with nary a problem. I know we are in the minority, but just though I'd share.

I meant to add that it makes a big difference how far you are sitting from the TV, how big the TV is, and just how high it would be mounted. So much to consider.

I've always thought it looked tacky, to put a TV above a fireplace! A fireplace is a beautiful focal point of a room. The TV is a TV. Not a decor statement. It takes everything away from the fireplace when placed there. Why would you want to do that? A TV belongs on a TV cabinet or an entertainment wall unit.

No it’s not tacky, if it works for the family then it’s fine.
I have 3 fireplaces in my house that I don’t use unless we lose electricity.
I also think tv cabinets/entertainment wall unit is outdated as heck