I get like that as well and often think why don’t they make a 2 page type setup for locked heros and unlocked heros with same amount on each page.
All new heros come to the current page where they are stored now and when you lock hero they are moved to a new area/page. When you click on level it displays the unlocked heros below it.
I have 75 slots in my storage and 67 of those are 3 and 4 star locked heros (and getting shorter) which means when I am training I have to keep leveling every 8 which makes it impossible to create groups of 10 for leveling.
If locked heros where on a different page with the same 75 slots then thatvwould free up those other 67 slots for collecting leveling heros.
I know I can purchase extra slots and I have but it would so much cleaner to seperate them rather than stuffing everything on one page.
Even better seperate page for each element or each 3/4/5 star hero woukd even be a far greater bonus but that would asking a bit much I think, lol.