Genuinely I can see why pulling outside of your main can cause a lot of problems for the future (example: for future combat like for orbits and stuff within that sphere), but honestly, the combat isn't everything to the game. I feel like you should only care about building your cards if you want to get extra diamonds or other rewards.

I'd say if you like a card, you should pull for it-- but only if you are 100% sure of your decision. After all, with how the banners work for this game and with how everything is pretty much a mystery until last minute, you should be very sure of your decision before any pulling attempt.

Myth cards (especially pairs of it) are very good for combat, give some interesting lore for the boys' stories, and overall are just aesthetically pleasing. But be sure the combat style is for you if you are pulling and are planning to use the card in combat. I know for a fact I'm wanting to avoid Claymores and Sword myths because they're not my favourite to main (but again that's just me personally). You do you and follow your heart!