I'm not sure where you read that Boma doesn't do GF well because every review I've ever read puts it near the top of the best places to dine GF list.
Our favourite CS locations are
AK: Flame Tree BBQ
MK: Cosmic Ray's & Columbia Harbour House
EP: Sunshine Seasons (must do every trip for us)
DHS: we really don't do CS here but in a pinch we'll get chicken tenders somewhere as they're available at several locations (we can't have the pizza at Pizza Planet due to other allergies but they do have safe GF pizza)
For in park TS, here's where we enjoy.
Epcot:
One restaurant that I was really reluctant for some reason to try was Biergarten but I was really pleasantly surprised. The majority of the items on the buffet is gluten free so we had LOTS of variety. The chefs for some reason seem reluctant to get fresh food from the back but when an entire section is free of our allergens I just go ahead and get the food from the buffet and ask for items that are beside unsafe foods to be brought from the kitchen and they always say yes.
We've also had good experiences at LeCellier but we're steak lovers so it's easy. Their maple creme brulee is gluten free.
We've eaten dinner at Akershus a few times and enjoyed it a lot each time. Chefs have gotten safe foods for us of whatever we wanted from the cold buffet and then prepared delicious entrees. I don't know what they have for desserts for those who are only gluten free but for our long lists of allergies we only had the standard cookies with dairy free ice cream or sorbet. I think the Rice Cream dessert may be gluten free though.
MK: We love the Plaza. We try to eat here every trip these days. It doesn't cost much more than getting CS but you get served rather than having to deal with lines and carrying your own food and the food is wonderful.
DHS: We've never had a bad meal at any of the restaurants. Sci-Fi doesn't have many options but what they have is good and we love the atmosphere. 50s PTC has lots of options including AMAZING fried chicken, though you have to plan on waiting a long time for it as it takes a long time to prep and cook. HBD has amazing GF crab cakes and they have other options as well if you're only GF (with our long lists it was more difficult but for just GF they're good). Mama Melrose had lots of options and the chef did an amazing job creating delicious meals.
AK: We've only tried Tusker House but we've had great experiences at both breakfast and lunch. We'll definitely be back. They have so many options for different foods than you find anywhere else. I think DD15's favourite food from last time we had lunch was a root vegetable medley that that chef created for her. I was quite partial to the fried plantains. They've got plenty of great variety.