So there's a couple different things to point out here.
First is, nowadays, most schools do light technical sparring. It also happens to be what's videod the most, because it's what people want to see.
Second is that if you just started, there will be lots of schools that (for legitimate reasons) may not have you spar at the beginning. You have to learn technique before sparring is really useful, and safe (opinions are debated on this but ultimately, it just means if that's the philosophy where you're going, you have to be patient).
Third is that you can absolutely get good at martial arts while sparring once a week. There is a huge difference between sparring once a week, and training once a week. You are spending the rest of the week learning the skills that you can practice implementing in sparring. Again, at least IMO, when you start off more time should be spent on technique rather than sparring, then as your technique improves that should start to shift.
Fourth is that "hitting the bags and other drills" should still be done at the gym (but can also be done at home). If you only do them at home, you're not getting feedback on how you're doing the drills, how you're striking, making sure your guard is up, your punch is correct, your footwork is how it should be, etc. It is incredibly obvious to anyone that's trained whether someone is self-trained or not, when they see them do bagwork.
Fifth is that I wouldn't call all TKD or karate mcdojos that phase out sparring, particularly if you haven't trained before. Plenty of those places do spar, and are worth checking out, rather than just limiting yourself to muay thai. You may even find that you like them more. Check out all the schools near you, regardless of style, and see which ones you feel fit you best. Most places will offer a free class/trial.
Finally, where do you live, and how far are you willing to travel? We may have someone here who has a recommendation for you.