The notion that there was confusion between a Hunter and a JP is preposterous. The cockpits are very different, control columns are different, no brake lever on the JP totally different windscreens etc. Etc.
305 knots is WAY above the speed needed to loop a JP, it could, with care, be looped at 140 knots with the gear down, but 240, 250 knots was more than enough.
Technique on the JP was to go to full power, apply 4 g initially and then check for a straight pull by ensuring the tip tanks were equidistant from the horizon, Hunter doesn't have tip tanks and the wing tips are well behind you.
That way the recovery height could easily be above start height and the gate height WOULD be achieved, and one could also tighten the loop on the way down by pulling to the buffet or 5.5 g whichever came first and complete the loop HIGHER than start height.
As for throttle friction, another red herring, his hand would have been on the throttle during aeros and if rpm had reduced as suspected, known, there would have been a noticeable reduction in thrust, another reason to throw it away and roll out at the top.
As for confusing the start height of 190 feet for 500 feet is also preposterous for an experienced pilot, regardless of altimeter readings.
Someone mentioned the effect of age on G tolerance, it certainly is a factor. In my youth,, as a JP. QFI I could sit through max. rate turns at 5.5 G without a g suit, no problem!
In my 50s I flew a couple of trips in the Hawk, what a difference even keeping a lookout going was very hard work, even 3 g in a Spitfire recently felt very different !
Sorry guys, the suggestion of confusion is impossible , for me at least, to swallow.