There are plenty of examples of both situations really, I think the main predictor of whether the devs end up proving they were right is when they have a really cohesive idea and manage to realise it well. The main sense I get from Bannerlord MP, unfortunately, is much more disjointed - some aspects are well planned, others seem more vague, and it doesn't come together. The class system and matchmaking, for example, actually work really well - in isolation. However, no further thought seems to have been given to the possible negatives of the system e.g. lack of customisation, extreme complexity in balancing across multiple game modes when gold is formula driven. We already see some of the planning get disregarded as the reality clashes, such as the original plan of unit aesthetics matching their armour and speed (Vlandian sharpshooters originally were tanky as they looked, now they have very low armour but still look like absolute units).
Most of all the lack of cohesive design and planning is apparent in the combat. I think it was Armagan who defended this saying they always wanted physics-driven combat that's responsive and enjoyable to play - but the lack of fine tuning to the combat completely marred this, if it was even possible. There have been many updates and it's gotten better, but it's all putting out fires - responding to individual issues with patches and slight tweaks, which leaves the overall state still disappointing.
The final thing I would say is a huge weakness in TW's approach to the game is eschewing any comparison or building upon Warband. They seem almost offended by the suggestion that cues or lessons could be taken from Warband, which to me just seems like a zealous desire to insist everything is built from scratch and re-thought from first principles. Which is admirable in some ways - how many sequels are just disappointing cash grabs that add 2 things but otherwise just re-sell the same game? - but in this case I think doesn't work considering how much unfulfilled potential Warband had. If ever there was a game that needed repackaged, polished, improved upon, and perfected, it was Warband. Instead they scrapped it all and made another diamond in the rough (and the diamond part is arguable).