SSRs are basically 6 skill levels above SRs, so a slvl4 Assault SSR will do as much damage as a slvl10 Assault SR. Assuming equal stats, of course. But LMB SSRs will (almost) always have more stats than SRs.Because you can farm Gem Quests with Half Elixirs, which you can then gain back from Gem Gacha, weapon fodder is just a matter of time. If you have LMB SSRs, level those up first (ESPECIALLY dual-skills, even if those dual-skills are not LMB!).
tl;dr; just work hard~