Agreed with Minato about the way formation skills works. Haven't pinned down the formula but the level requirement is just a minimum to obtain the skill. Additional levels in it are based on the levels and types of pet you have in your formation otherwise, but it does not require you to double up on the minimum requirement. Otherwise some of these skills would be impossible to get past level 4 or 5.
Also, I forwarded your suggestion on to Ian to pass to the Devs, Minato. It would be nice to see Pet XP cards available elsewhere.