As long as you can find a car through Motability that you are happy with, and the only option that you will consider is a lease, then it’s pretty pointless looking elsewhere. Motability will always be cheaper due to their block 20% VAT exemption.
However, leasing is just one of many ways to source a car. The majority of private buyers don’t lease and, of course, the overwhelming majority wouldn’t even entertain the need for a brand new car. There is life beyond Motability for those who have the means and the confidence, and far cheaper ways to run a car if you don’t insist on a brand new one!