So the USTA agrees apparently that different areas/sections need to handle things appropriate for them. The big challenge, is with leagues that can advance to States, Districts, Sectionals, Nationals, at some point these different approaches come together at some point and the mismatch is going to cause one problem or another.
In Southern for example, not every state has early start leagues. So Southern taking the approach to allow players to play at their pre-bump level through Sectionals arguably puts states without early start leagues like North/South Carolina, at a disadvantage because they have only at level players, while a team from Georgia, Alabama, or Tennessee could have a roster full of now above level players. But, the (correct IMHO) National rule means the winner of Southern Sectionals may very well have Nationals ineligible players so the team going to Nationals isn't representative of the team that won the section. That Carolina's team that would be fully eligible may be the better team with just eligible players playing, but they lose out.
The sections that require immediate promotion to the new level do make things more fair for 2019 competition as only at level players are playing, and the teams will be fully eligible for Nationals, but it really puts captains in a bind as they could lose a good portion of their team, and they have no way to know what their risk is (ok, well, they could get a report from me
) so it is a bit of a gamble like you say. I think this is fairer than the alternative, it keeps the competition for the general population competitive rather than having a Nationals ineligible team wreaking havoc through league and playoffs, but still isn't ideal.