Agreed, powerbanks recharge phones, flashlights, buds, tablets, and with USB-PD coming also laptops.
I think in the last >20 years of phone ownership I did a battery case once, never did it again as it made the phone too heavy in pocket, better to attach a Powercore when needed, and with Anker making many types of Powercore you can go for fast or cheap recharging.
Warning: if you put a heavy external battery as a case then you make the total energy of impact higher when that heavier package falls to the ground. If you have light non-battery case it protects the phone.