What a complete misrepresentation...

Limiting notice period to two months and forcing you to give customers the possibility to terminate at any time is not killing ARR. It might moderately increase churn but even then, unless you are frankly dishonest, not that much.

You still have ARR when your customer can terminate their contract.

Even yearly discount which the article presents as done for are still a thing with the possibility of early exit. You just put a clause indicating that the discount is forfeited if the customer leave before the end of the contrat. Phone companies do that all the time.