Well I agree with the last bit. As for that internal rhythm thing, not speeding up between parts of a tune, etc., I found that recording myself was instructive. Like wearing a hair shirt. Of course, not everyone will be their own best critic. Let someone else have a listen too, a good musician, and give you tough love. Metronomes are like stabilisers on bikes, except that we're not toddlers and we can't learn like they can. The best metronome on the planet still lacks the humanity that is true music. Not a small thing.