At least you've gotten rainbows in the past. I started playing shortly after launch in June and just got my first rainbow (Gilg) on the People's Choice banner last week! I am purely F2P. I just have really bad luck when it comes to this game.
I finally finished Cecil's LB. Recommendations of who to dump LB pots onto now? If I had Noctis, it would be him, I know.
Ling has a solid scaling fire imperil on her LB, but you're probably better off entrusting her gauge away to someone else unless you've built your team around fire damage. Garland gains a +atk buff on his LB with his 6* with the same scaling as Cecil's LB, which would be an ok option to have if you're going to use him and replace Cecil with WoL as your primary tank. WoL has the same scaling +def buff on his LB, but it really isn't worth it. There just really aren't very many LBs worth leveling atm, and there won't be for a while. Looking at future releases
Tidus - scaling water imperil
Wilhelm - scaling % damage reduction
Rikku - scaling def/spr buff
Prishe - scaling def/spr break
KDelita - scaling atk/mag break
DVeritas - scaling def break
FVeritas - exception to the usual rule of not leveling pure damage LBs because his LB just hits so goddamn hard
EVeritas - scaling % damage reduction
I'll stop there, basically starting with the first Veritas batch it becomes much more common for units that people actually use to have an LB worth leveling.