I think voting for features in its current form is good since it allows Monzo staff to easily see what the Community want, even if what they want isn’t currently feasible. Yes, there will always be long term ideas or ideas which Monzo can’t or won’t implement with loads of votes, but so long as people know that it is just a guide for Monzo and not a guarantee that features will be built I think voting is good community engagement.
Voting might also bring small things that were mentioned on release or labs threads, but seem to have slipped under the Monzo radar, to their attention. For example, setting a target date for pot goals, adding notes to transfers on iOS and entering international transfer amounts in foreign currencies. If Monzo created a new Trello map equivalent these ideas could still be lost and never reach the map.
I do like your idea of the Community voting every few months for one of a few features for Monzo to try to build, but I think that could work well alongside the current voting system not instead of it.
NB: maybe this “is voting a good idea” discussion should be split off into its own thread.