Not beholden to the same level of expectation as main-line series
When you make a new Star Trek series, for right or wrong, there are a lot of expectations that come with it. Whenever it’s aired, the franchise has always been one of the most well-made series ever, and fans have certain expectations that come with it. Part of the reason why the newer series are so polarizing is due to the expectations fans have of the series.
It’s both its greatest strength and its biggest weakness.
If you do another film that connects to the television series, you’ll have the fans of “Nu-Trek” waiting to evaluate it to see if the film lives up to the established norm and you’ll have the detractors of the new series ready to tear it apart just for existing.
A new timeline, or keeping the one currently established in the Kelvin timeline, is the way to go. Fans won’t be as critical and there will be more room to breathe with fans due to the fact it’s not canon to the current crop of series.
Otherwise, the fans will miss the forest for the trees and will be even more critical of it than they would otherwise be. Believe that, by the way. No way will these films not be super analyzed for all it did wrong. So you might as well cut off part of the criticism already by making it devoid of any connections.