I don't use LR on an iPad or an iPhone but am considering trying it for certain tasks.
I use LightRoom Classic on an iMac Pro most of the time and it runs pretty nicely since Adobe began accessing/using GPU cards.
I use a 13 in MacAir from 2018 for travel, and, I agree, it is slow, and marginally acceptable. The new M1 Mac Air is probably significantly faster, but before I jump the shark, I would like to know how they compare. With a shift to RISC processors coming, I don't want to invest in more Intel iron without a clear understanding of what that entails. I lived through the shift from water cooled Power PC chips, so I have lived through Apple's swaps in hardware processing chips before.
I find the future very promising, but may be slow to jump aboard until I have a clearer understanding of everything that the future entails.