If you've got an LG OLED this is simply not true. I have a C8 model and it's WAY faster than my roku or PS4. It's awesome and the app switching is instant. There's no start up time at all. I HIGHLY recommend using the built in apps on an LG OLED with WebOS built in. It's great.
As for HBO, I buy it as a channel within Amazon Prime so it's accessible through the Amazon app on the TV. Problem solved and it's one less account to worry about.