So has a fairly new player, I gathered from this thread that i should focus myself on the eidolon first.
But isn't focusing on the SSR weapon first be better ?

Mainly for the fact that you need 10 weapons and only 6 eidolons, plus you have even more diversity to worry about with the weapon type & element as opposed to just the element for the eidolon.

Lastly it's cheaper to MLB weapon rather than eidolon, considering that I have to do both event at the same time, that's also quite important.

Am I wrong ?