Smart alecks like to say that Steve jobs didn't invent the first iPhone. Smarter alecks love to mention that Apple didn't invent the first touch screen device.
But Apple was the first to get the details right.
They understood that smaller devices need to be faster than desktops. That's because people have warped expectations. If a mainframe takes a day to do something, then you'll leave the room and come back later. But smart phones that take that long get chucked.
This inverse relation of speed and device size is contrary to expectation. After all, the original iPhone only had 128mb of RAM. Your typical desktop is faster. But people need their phones to be quicker than their PC. They're impatient.
Making a fast UI isn't free. It's an investment and time is a precious resource. Put bluntly, "hard" tasks can be a little slow but "easy" tasks need to happen now. It's all about the user's perception.
Business Saas? It can probably run a bit "slow." Employees will be, at some level, paid to use it. Instead, focus on capability. That will deliver more value.
Your B2C idea? It's gotta be lightning fast or people will lose interest. They want it to be likety-split. Speed will be prioritized so long as its good enough.
Time is precious when building great products. Spend it wisely.