I don't think this is just a result of Supergirl. I think that film is (more or less) exactly what the director (Craig Gillespie) wanted. It just think something went wrong, Gunn tried to help, but it was too little too late. The film gets a lot right, but it misses in some big moments (as you've pointed out), and ultimately a just fine but not great film.
I think this is a result of pacing and releases. The merger was expensive and Skydance needs money. Putting out one blockbuster a year, and in the case of Supergirl a blockbuster that severely underperformed, isn't going to work for the studio.
The question is, how much rushed crap are we going to get going forward? Hopefully little to none, but I suspect we'll get some rough films. (But maybe some great ones?)