I don’t agree that mats should be available to buy from the gem store. I am a spender myself. Not as much as some but more than most. I’ve been playing since last June? and just now ascended my first 5 star with two more on the way. I will say it would be nice if mats dropped more frequently and it does feel as though the elemental chests have been nerfed. Although I have no evidence to prove this.
If mats were available to purchase in the store new players would literally buy their way to the top and this is not how the game is set up to be. Players that pay have slight advantage now and they offer special deals with mats often enough I believe. You brought up food and feeders. Trust when I say I have talked to big spenders that would gladly buy enough summons to get feeders and pay gems to refill their food if mats were available to buy in the store.
The only solution I see is a request to increase mats gained through game play. This benefits the whole community and possibly the p2p more as they will actually have the heroes to spend the mats on. I believe there is already a thread in the ideas/suggestions area. If not you should create one.
Above all the game is meant to be used as a fun pass time. If you were able to fully level a 5 star team in under 6 months, to me at least, it would take away the sense of accomplishment. I feel like I will appreciate my fully maxed 5 star team more because I have put in a great amount of time to get them leveled.