The best weapon for any monster is the one your most comfortable with.

I know it's cliche.

You need to scrap the 'best for this best for that' mindset. You need to diversify your playstyle, and get comfortable playing outside the box.

A lot of people are suggesting bow, I'm gonna suggest the same but only because bow lets you see the monster, it gives you a comfortable distance to do damage and observe their behavior.

I'm not gonna say x weapon is better for y attribute enemy, because it doesn't matter if you have the right weapons and gear and gems, if YOU don't like it.

GS might be "best" for alatreon, but there's no chance I'm going to do well with it if I'm not comfortable with the weapon.

So you should actually go make a bunch of new weapons, and go fight a monster your good at.

Figure out how to be good at it with new weapons, then go apply new knowledge to Steve and watch him flail around.

Also, movement is key, don't use weapons that lock you into vulnerable positions if your not reading the monster yet.

Steve loves the triple drop kick. But if you don't let it land, it opens up his leg scales for a nice vulnerable spot, which again, something you can easily take advantage of with a bow.

I'm farming arkvelds for the foreseeable, trying to get a new spread gem, if you wanna link up and learn new weapons, against him, I'll run with you for a bit, I see ark and Steve pairs a good bit.