I agree. I will admit that I myself have fallen into disappointment/impatience regarding certain features, partly because of the early Trello board timeframes (prior to the CA switch).
I think Monzo have learnt this themselves too. Perhaps being a bit more vague about longer-term idea implementations (still transparent about intentions however), whilst focusing on one thing at a time, would be a good route to follow.
I think transparency is fine as long as customers remember 
Monzo is in charge.
Take the endless requests and reminders about Apple Pay. It’s not like Monzo will have forgotten about implementing it, and it won’t appear any quicker because of the constant prodding.
The demanding because of the transparency makes customers appear entitled and unreasonable.
If Monzo haven’t yet implemented a feature they have promised, and it makes your use of the account impractical, simply wait until your feature is brought in. No need for endless stropping off to Starling or moaning.