There is such a thing as tennis players inventing strokes. ( I heard that Borg was told to forget about that topspin. )
One problem with inventing a stroke vs imitating a pro stroke is that if the invention is not sound biomechanically you might get injured. The shoulder is especially vulnerable to injury, including impingement injury.
The problem with having your tossing arm still up at ball impact is that your shoulders are very level which probably means that you cannot forcefully and safely use internal shoulder rotation
for racket head speed. The line between your shoulders looks level in that photo.
See the Todd Ellenbecker and Jim McClellan videos on this shoulder risk - shoulder impingement on serving especially with incorrect shoulder orientation. Reply #4. Basically the line between your two shoulders and the upper arm bone at the shoulder should not have a larger angle as detailed in the Ellenbecker video.
A sound pro service technique using internal shoulder rotation:
Note how the line between the shoulders lines up with the upper arm bone (between the shoulder and elbow). The upper arm is not quite in line but nearly - a small up-angle for the upper arm is OK according to the Ellenbecker & McCellan videos. I'm not going to estimate the range of small angles being used by the pros - judge for yourself by viewing single frames at impact when viewed from behind.
Also what camera did you use to get the picture?