The sword isn't a big upgrade, it's just a little better than an SRs weapon at max skill level and require 2x fodder to max skill level, so if you low on resources and can't get both weapons just get the lance and leave it in your inventory until you can leveling it or you'll miss one of the best free SSRs weapon, while you'll throw that sword out later.
If you keep play, you'll eventually able to do guild order and have plenty of resources but that lance only come once. Just remmeber to do gem gacha everyday.
The lance without flb is still much better than the sword. I think you only care about the stats, but skill is the most important part of a weapon.