Hoard cards and difficulty

From what i can gather, it’s not worth playing hoard or escape on anything higher than beginner or intermediate until you hit level 10. Until you hit those level locked skill cards, you don’t get anything more than common or rare anyways, so in terms of progression, the extra work is wasted. Higher difficulties just have point multipliers so it doesn’t even translate to extra xp.

Also beyond the 10 base skills for any character, has anybody seen a hidden earnable card?