Start dates are only available in paid plans so you can’t have rules about them in the free plan. Feel free to vote for that feature here (for paid version at least):
Asana has already committed to improving this soon in numerous posts in the Forum over the last days/weeks.
The My Tasks update is an example of the opposite–Asana maintaining the functionality previously available, albeit I was not a fan of doing so with fast follows instead of just waiting and avoiding frustration like yours. I can’t think of many examples at all of them pushing features to paid.
However, the feature seta of the various paid tiers have broadened substantially. For individuals, Premium is more compelling now than earlier iterations of Premium vs. Basic, and for organizations, the same is true for the current Business over earlier versions Business vs. Premium.
Larry