4*s are basically worthless, except for event 4*s. You can buy 5 fresh 4*s for 2 te during step up pack events very easily, and with only moderate difficulty during all other times. Also many events hand out 2 or 3 4*s for very little effort to participants.
The vast majority of 5*s are worthless, except for those with speed or skills suitable for BA/Guild/Colo. If you just need generic 5*s to fill your roster, cards like Klavier, Zita, Soldado, and Purifica are only 3 TE fresh if you shop around. On top of that, the odds of getting a 5* from a 4* ticket are so low it's not really something you can count on.
Getting a 6* from a 4* ticket is so ridiculously rare its not even worth contemplating.
Leana points on the other hand give you a 20% chance at ambrosia which is something most players need, buying ambrosia is extremely difficult as you risk getting scammed unless you are willing to waste time negotiating collateral, you can get event items which can be helpful depending upon the event, and you have a slim chance of getting an Edwin, one of the few useful 5*s in the game.