I know for a fact from before I started kegalling that no matter what I did, even if there was nothing to arouse me (visual stimulation), I would still finish quickly. Just like you are saying. Edging, kegalling, and reverse kegalling got me to a point to where I could at least last 5-10 min without finishing (with no visual stimulation). Once I had visual stimulation added however, it was as if I hadn't accomplished anything, and I found myself finishing right away.
At first I had imbalanced floor muscles (PC/ BC) and when I balanced them I could last longer. It is when I had balanced floor muscules that arousal techniques were really beneficial and could help me last longer.
My frenulum is still as sensitive as the day I started here, although I have learned to lessen the intense arousal effect it has.