As you note, the hill sprints are a sport specific power workout. The strength/power they build, provided you do them well, will supply the strength base for more effective ME. There are a few common reasons why you might not have seen much benefit from the hill sprints:
1) You can’t sprint. This is a big problem for slow twitch endurance people. They can’t even recruit all the muscle mass to really sprint. The ST fibers they recruit don’t get tired in 10 seconds so they feel like the workout is a waste. But learning to push hard and recruit more FT fibers that DO become fatigued in 10sec will build more sport specific strength and power. The easier these workouts feel for you, the more you need them. Sprinters can destroy themselves in these workouts.
2) Your hill is not steep enough. 20-25% is the minimum grade to use for these. 30% will do an even better job for mountain athletes.
3) You need more resistance. If your hill is not steep you need to drag a tire or a dead animal carcass. Even a weighted pack or weight vest will be good.
The strength base gained from these is not essential for doing ME. You will still get good gains from the ME but you’ll get more benefit if you are more powerful to start with.