4 star mats are supposed to be rare. Still if you finish every rare quest, you should be able to get a fully ascended rainbow team in about a year…faster if you purchase mats or get even reasonable luck - but still not a lot faster. The game is designed that way on purpose. Otherwise everyone would be walking around with an army of maxed out 5 stars.
People who say loot is nerfed haven’t been tracking things carefully. I’ve been playing over a year, and loot hasn’t been nerfed aside from the raid tourney, which is 1) a whole new way to get AM’s and 2) will be unnerfed eventually. In fact there have been many new ways added to get AM since I started playing.
For reference on ways to get AM’s and a reasonable straw man on what a F2P might expect: List of methods for acquiring unfarmable ascension materials via playing / Where to earn nonfarmable ascension materials through gameplay