Your idea would require usage of multiple pokemon. Don't fix something that's not broken.
But then complain for a series becoming stale and lazy?! Not sure why you would think it would require multiple pokemon?
There would be too many changes to moves to make
I agree, this is probably the real issue. It could be very tricky trying to balance such a wealth of moves. However it could also help diversify the plethora of samey moves. But yeah could be a lot of work for a relatively minor change.