but I've always struggled with gearing them.

this is the case for most people; gear and molas are usually the bottlenecks.

as for your other question, take a look at a characters toolkit and think about what its primary role is before you try to deduce what stats best assist that role. roana for example is an ssb counter that has a heal that scales with health. her s2 is a passive skill and her s3 isnt that strong since it doesnt revive dead characters/buff can be dispelled(though the heal is nice). because she does not need to cycle turns quickly since she gains more out of her passive than her skill usage, people are putting her on a counter set and aiming to get as much hp as possible.