They said that refreshing witb donuts will increase the chance of getting different types of things but I think they also lower that chance for refreshing after lvl-up. I just lvl-up and got only 2 items from event. Not nice!
I reckon it would need a sample size to be able to compare the difference between the amount of collectables that appear now for different hero levels. Unfortunately that would end up being quite an expensive experiment as it should be done on multiple accounts. Are you now comparing a single refresh you made to what you used to get/felt like you used to get? Or did you refresh all the mission zones multiple times?
I don't care about refresh with donuts from this update, I am interested that they should not lower chance when I can refresh missions with new lvl-up.
To my knowledge there is no evidence of the chances of collectables in missions after a refresh to have been lowered. It's unfortunate that you feel like this has happened, but with no vast experiment they are only assumptions. I find it difficult to believe that this change would've been announced if it wasn't really the case.