Hey Slicepong!
Yes you’re spot on about deep balls and open etc. I can understand the hesitation on half long or mid court balls like you said, definitely pushing doesn’t have to be a wasted shot if you are aggressive with it and go for good placement, maybe take a look at this video for more info on that area: https://tabletennisdailyacademy.com/videos/how-to-make-your-long-push-more-effective/
I would say the flick is a good choice if the ball is slightly higher and you are confident of controlling the spin and being able to play a positive shot to put your opponents under pressure, otherwise a good quality push would be good.
I think most players would say they find pushes easier to control direction, although now the backhand banana flick that many players use is great for creating a lot of spin and therefore control in the direction. I’d suggest getting really confident pushing with better quality and direction and then gradually add in more flicks as and when you feel ready.
