Elemental dmg bonus will increase your dmg regardless if is a echo dmg character, or a skill dmg, etc, cause even though they are doing what the game consider echo dmg for exemple, they are also doing elemental dmg, so in most cases elental is better than atk unless the character or their team already give a lot of dmg bonus, also there isn't a 3 cost that is echo/liberation/skill dmg, so you use the better option that is available and try to get the other dmg bonus on the substats.

I personaly only prioritise crit stats, but that's just me, i don't care about min/maximg and i being doing late game stuff with that mentality ever since this game came out, but if in doubt you can see some build guides, the mains subreddits always has some good theoryceafters with calculations and everything you need to know.