My parents and teachers gave up on attempting to assign me homework and make me do it. I despised homework. Interesting assignments were great! But day to day homework? Never did it, which isn’t a good thing (and this isn’t me attempting to brag).
The only reason they stopped is I was getting top marks in every subject anyway, and the only reason I had that was I had a tutor who pushed me so far beyond high school level that I was finally interested in the topics again.
The neat part was: to learn those topics, she gave me a crash course of most of the year 11 and year 12 curriculum in 3 or 4 months or so, because I needed the base knowledge to learn the cool stuff
If the kid is doing the exactly same exercise for fun during holidays, then the issue is not the exercise is not interesting for that kid.
Most kids with good grades don't have tutor, unless they struggle a lot or it is before entrance tests for high school and college.
That does not sound like exercises themselves would be bad or that he would cease to be interested in learning overall.
It more sounds like after many hours at school, he wants to do different things that day. But when school is not present, he seeks similar activities and his willingness to learn is not deteriorated. That kind of sounds healthy and not wrong at all. In school, kids spend a lot of time learning or doing focused activities, a kid wanted to just play after that should not be sign of something grave.
The only thing that is wrong or unusual is the hours long fight against homework. I dont think that is normal for majority of kids. Only some parents I know report that much daily fights, most have fight here and there once in a while only.