Given that a fair chunk of the purpose of the line is to link to the boat, it seems like someone didn't think this through properly. That connection has to be reliable.
Does every station always have passengers? Would it be possible to eke out a slightly shorter running time by making all the intermediates other than Brading request stops, and fitting bus style stop buttons to the units?
Do the units have very slow doors like the LNR 230s? Could replacing the door mechanisms (or even the whole door setup) to something that operates faster such as a two-leaf plug arrangement, plus switching to driver release, get a couple of minutes off the run? You definitely could on the Marston Vale.
If you could get both services reaching the ferry, then (at the expense of a slightly slower journey and a bit of waiting) offsetting them by 15 minutes would make the connection largely reliable. Given how many tourists use it in summer and given how much tourists faff and get confused, this might be better than a "Swiss style" connection with almost no slack in either direction. If there's some sort of shop and cafe in the terminal that can easily deal with a 15 minute wait for tourists.
There is no scope for making any of the existing stations request stops - I would think it would only be at Lake (and Brading, where the train stops anyway) that you would regularly see no passengers.
The doors are a bit slow and clunky, but not such as to be a material factor.
The basic problem with the two-train operation is that the passing place at Brading is not halfway down the line. It’s a mile nearer to Shanklin than to Pierhead. That is why the second trains are not running at precisely 30 minute intervals to the core hourly service - they run 3 minutes later up, and 3 minutes later down. And these timings do indeed make it difficult to run the second train up the pier at present.
All this is a far cry from the regular 30 minute service that was trumpeted when the new trains were inaugurated. Whether experience will allow timings to be tightened up remains to be seen.
The suggestion of more leisurely connections might be welcome to tourists (there is a Costa cafe at Pierhead, though still closed during covid) but not to locals. And it ignores the hard fact that the catamaran service is hourly, with very few exceptions, so the same train has to deliver and collect passengers. No scope for hanging about.