You have already got the speed , focus on spin man. Speed is overrated in table tennis ... and spin is underrated
.... focus on your timing , where you can generate more power ( both spin and speed ) without putting in so much effort , focus on your footwork that you are able to get into position faster to execute that timing , focus on practicing different timings , A, B, C, D ... ( you can find them in different places in the internet ) and also focus on hitting the sweet spot of your blade every time you touch the ball ... the issue with your waist rotation others have already pointed out ... and don't DON'T GET A FASTER SETUP .... you will lose feeling and even though you will win some cheap points at the onset it will stop your development ...
Now as to your original question ... first focus on increasing the spin and understanding the spin of the incoming ball .. and adapting your loop to it ..
I would say start practicing more loops against backspin , both slow spinny loops , and third ball attacks where you take the ball earlier ... but make sure you mix it up with looping against topspin as well ... essentially , as you increase your ability to spin you should also keep in mind that your loop ( starting position / timing etc ) should be able to adapt to incoming ball ... once you get that and once you are able to start placing your loops on dime , then think about speed ...
when ever my brains goes all speed demon , I keep telling myself to remember that in table tennis the one who wins a point puts one more ball on the table than the opponent with smart placement , and spin actually helps you do do it , where as speed does the opposite .. its easier to block if it does not have enough spin and the ball comes back faster so you have less time to react to the returning ball ...
