Decrease the rewards from Raids
I think part of the problem with Raids is that the reward is too big for the effort.
Instead of giving all the rewards for defeating the Raid Boss, give options. List the different (possible) rewards:
1)TM (RNG for which type you get)
2) Rare Candy
3) Golden Berry
4) Chance to catch the Raid Boss Mon
5) A free Raid Pass (new item)
Then using the formula that calculates how BIG the reward is now, use it instead to determine how many choices the raid winner gets. 1 or 2. No more than 2 can be chosen for a single raid. The player picks the reward(s) they want.
This will still give nice rewards, but a lot fewer of them. It also gives the player some involvement, and makes them think through their own goals.
Answers
I feel like the rewards are fine as they are. I'm not exactly rolling in TMs (1 of each after 20 raids), and I've seen only 1 level 4 raid.
Usually I'm just getting a bunch of revives and a few rare candies, but the potential rewards keep me coming back. IMO Niantic did a good job with this feature.