This game is based on rng. Everything is based on rng (drop rate, upgrade rate, etc).
When it comes to Upgrade System, sometimes rng is really sh*tty, I mean u spend that much money and get nothing, u can see guys with good upgraded gear, but they either cash or they grind a lot (some chinese use bots). In some MMORPGs, upgrade isn't based on RNG. It should be like that in DBOG too - and it would make it a little easier. For example: Everytime u try to upgrade with blue/red stone u get +1 potential, when u upgrade with purple/green and white stone u get +3 potential, etc. So it would mean, u have to upgrade as much as you can, and then u will have more chance to get Success. Some people already suggested this, but it didn't get any feedback, so I decided to try.