What you're experiencing is 100% normal for any electronic device.
Components get very hot when running memory intensive programs and they can't dissipate heat as quickly as the components on the board generate it.
Either the official bumper, the Poetic bumper, the Nikkin hard slim case or a TPU case.
I have all but the OEM bumper, but the other 3 are so easy to take on and off, not a pain whatsoever.
I bought it right away when I found out about it.
Then about 15 minutes later I thought to myself... wait a second, I just spent $71.76 on a phone charger...