It is possible to loop this ball by using "brut force", meaning as described by Pnachtwey, by reaching a very high paddle speed..........but it is also possible to loop this ball by touch.......has you described, by reaching a high dwell time (= "grabbing" the incomming spin).
Touch is everything in table tennis. I have faster arm speed on my FH loop than many of my team mates in my tt club, but a team mate is able to input incredible spin, more than me, even with is "slow motion" FH loop. He is able, thx to his touch, to deform the rubber even on "slow motion" strokes.
See this video of Shlager (serves) :
I do believe that anyone here can reach far higher bat speed on a pendelum serve than Schlager is using for most of his serves here. But nobody here is able to imput has much spin than Schlager. Thanks to his amazing touch, Schlager is able to input more deformation than us to his rubber, resulting to more spin than anyone of us, he is maximazing dwell time. And this is what you explain also at the end of your post, the acceleration is an important factor to reach a better dwell time/rubber deformation/higher spin.