we need 1000 iron and 1000 wood to swap from a "mastery" to a different one of the same rank.
No problem here, unless you are short on Crystals. If you are short on Crystals, you can't swap; you'll need to cover the need for upgrading an ability and, then, you can swap again paying no crystals at all.
This is blocking me. I can't upgrade or I can't swap stats!
Add an hint into "Hire" tab of Dojo to advice about hiring limitation: if you Hire a hero, you can't get 3* in that run!
you can't swipe ==> you can't swap*