Mac OS, like Windows, has fundamental latency and battery use issues that can't be easily fixed without sacrificing backwards compatibility.
> Decent PC or Mac with SSD is much faster than iPad
Yes, but speed isn't latency and hardware speed is irrelevant.
My DOS-based 286-12 had better latency than my Surface Book and MacBook Air do, mainly because DOS has no (or very little) multitasking. My iPhone also has excellent latency as it limits the APIs available to background tasks, stopping the typical 'Windows Search Service' (or any other random background executable) killing foreground performance.
The ipad is not magical. Were you to run actual dev workloads on the machine itself it would be sluggish with terrible battery life.