I noticed the coin upgrade cost doesn’t show any longer until you go view the skill directly in the skill selection menu rather than in class selection window.
I believe this is what you were looking at, that it would buy the selected highlighted skill card, if you had enough Gears Coins and if they were not maxed already. It seems you shouldn’t , and instead view them through card selection screen. There was no such thing as buying class levels anyway.
I think it’s a UI display bug as I remember coin cost showing if you hovered over the skills in the class selection in Op 4(eg the menu showing the class level, description, etc,). Doesn’t do that now and you have to go into skill selection itself to see the coin prices.