you're logic is not credible bc you're basing it off of subjective beliefs. Kakshi's prime is literally when he's most powerful, regardless of Time-limit/hardworkDo I need to? Opening the 8 Gates takes hard work and special talent. It's not something everybody can learn or do.
Compared to Kakashi literally doing nothing, and Obito conjuring himself from limbo back to the physical plain, in order to give Kakashi a power up with a 30 second time limit. That Kakashi can never do again.