From my point of view, the cause is different:
1. Lack of design a.k.a. designed by coders > At 5 months the team has happy path coded the entire feature list, the screens are ugly and non-intuitive, ...
It's obvious, that the product wasn't designed. Feature list isn't design. Competitors app isn't design. When you have UX/UI/API designed, it doesn't happen that the result product is ugly because of the lack of time. Lack of time may cause, that there will be nicely looking, but slow/incomplete/unreliable product. You need blueprints before building. It can be designed upfront by one designer who is in contact with user and stakeholders. When not, it has to be designed during coding by software engineers which are drowning in technical details and cut off from users. So just having some more time wouldn't make it a good product.
Also with some plan, they could have created estimation based on something. That would help them to get a realistic timeline.
In the end, the boss and PM should have known better.