As with many things, doing things to the latest safety standards means things aren’t quite as slick.
I wouldn’t say the 484 door cycle is particularly slow.
My money is more that the Brading loop simply isn’t in quite the ideal place. Politically I can’t see the 20/40 service returning given the money spend on Brading.
I assume a lot of the current problems with Wightlink/Island line connections is currently due to the rebuilding works at the ferry terminal at Portsmouth Harbour station. I don't know when these works will be completed.
Notwithstanding these remarks I have the following suggestions for improving scheduled train times on the Island: -
(i) Let the driver's release the doors at each station, even if the guard's still close the doors. This will save time as the driver must know if he has stopped at the correct location at each station. It will also ensure the guard's can spend more time checking and selling tickets instead of rushing off to release the doors at each station. I assume that this could be readily arranged as the D78 vehicles, were configured for OMO on LU.
(ii) Where practicable increase the permitted line speed above the current maximum of 45mph. This was as I understand the max permitted speed of the tube profile trains previously used. The former D78 vehicles now used on the Island line have a max speed capability of 60 mph, see unit data panel on vehicle non cab ends.
(iii) Others on this group have mentioned the slow speed of the single leaf door leaves. I think one way to improve this situation is to replace the pneumatic actuators with an electric actuator, that could be designed as a straight replacement for the existing actuators. Please note it is not reasonably practicable to replace the existing single door leaf with a bi-parting door arrangement. There are no door pockets for the door leaves on the D78 vehicles available in the main window bays above the bogies. To introduce one would require a very extensive rebuilding of the body shell, that would be very very expensive!!!!