If you really like him, then yes go ahead, regardless if he's weak or strong. If you're pulling for who's stronger. I'd pick nahida (even though she's not a dps) as she's coming in the second phase of 5.1. Though it kinda depends on what role you need right now. DPS? or support? She's that cracked but kinich is still a solid choice. It more of depends what you want or need.
Pulling for meta is boring, and this games easy enough to clear anything without the meta units, I took a break during fontaine, So I don't have furina, neuv or arlechino, and i clear everything, just pull for what you like
Pull for who you like. If you care about meta, then pick nahida like the first person said. She can literally fit into nearly any team. Or you can save up for 5.2 and pull (probably) either arle or neuv.
Easily. A raiden / nahida / kazuha / xingqiu hyperbloom team destroys teyvat. A more f2p option is Raiden / Xiangling / Xingqiu / Bennet national team. These teams can easily beat the crap out of the abyss but it depends on your builds. There's also more raiden teams that should have no problem clearing the abyss. Those above are just examples.
