It depends on the school who you spar. You will almost guaranteed spar better guys if you spar at a combat sport. They will be better if you spar hard. They will be better if you spar light. And you will have more immersion in to what is required to fight a full contact fight if you are around full contact fighters than if you are not.
I would prefer to go to a school that has that depth of experience even if I don’t take it to its full potential.
So if your chronic fatigue holds you back from competing that is fine. But the fact the school has competitors will mean you get more out of that school.
The downside is you may not be comparatively very good in that school.
So for example this is Tiger Muay Thai. And it is easy to use as it is a very prestigious school and so there are a lot of videos and information I can access.
Now this school develops some of the best fighters in the world and does classes that would probably end us in hospital. But it also doesn't. It also provides a vegie patch where we could move at our own pace. The difference being the trainers are just better with a greater depth of experience in what they do.