With 4* in normal gacha being nearly as rare as 6* in FG gachas the ticket option seems to be the only way. But something tells me that only reliable way to get 5* for me is events and reissues. And with my luck 6* will drop in like 4-5 years (assuming managing to somehow drop one 10+1 pull a month), heck I failed and got 5* on the special 50% chance for 6* ticket thingy khekhe. I am an atheist in real world and RNGesus seems to know that and hates me because of it
EDIT:
Just for lolz I dropped total of 55k normal gacha shards on 10-pulls. A bunch of 3*, 5 lvl manyus and actually two 4* both of which are copies of girls I already have. After one of them I remembered your advice and dropped my last 5 FGs on a yolo single roll. Well I did get a 5*, only issue is that she is too a copy of girl I already have hehe (Water Lily to be precise). At least a cherry on top in all this is the fact that all three of those 4/5* girls gave me a skill level proc when "merging" .