I have been playing for a while and am completely stuck. All my 4* heroes cannot get to tier 4 because I do not get hidden blades, orbs of magic, sturdy shields, trap tools or warm capes. You can make nice offers for extra diamonds but there’s no point in spending any (more) money really because all I would end up with would be more 4* heroes that are stuck at tier 3. I have 7 (!) 4* heroes hitting that barrier.
If you want players to enjoy the game you must make it possible for them to progress. If you have crowded servers and want players to stop playing (and spending money) then you are doing a GREAT JOB!