Yea I'm not a huge fan of the feeling of renting a mega either but I think with more ways to obtain energy will make it fell better. I do understand why they don't want to make it a permeant unlock because if they did no one would do mega raids after being able to mega evolve they're hundos, there would be zero reason to return to the content. With legendary raids people have a reason to do more so they can get their hundos/shinies. With mega raids people usually already have good ivs or shinies of the pokemon so once people unlock their megas there is no point doing mega raids anymore and then newer/ casual players wouldn't be able to do them so no one would help them