There are a couple of problems here.
First off, a software development methodology is not a silver bullet. Just because you’re agile, it won’t stop people making silly decisions. Inexperience, lack of communication, poor management - these will bite you in the ass no matter how you do it. You sound like you’re blaming agile - I wouldn’t. From your description, I’d blame them for poor planning.
Personally, I feel agile helps prepare you for changing requirements, but what it will never do is make change painless. You can’t just suddenly change your taxi sharing app into a database. Your management should recognise this pain.
From my own recent experience, we’ve delivered an MVP for our a client under very stressful deadlines, we’ve burned ourselves out a bit and made a lot of awful hacks, to deliver it in the short term. However, currently I (and other consultants) are giving very strong advice to not continue pushing like this. Give us some time to redesign the MVP, fix the issues, and not work under strong pressure. I dislike arbitrary deadlines because they encourage short term thinking. The worst part is - there’s often no need for the deadline.
Secondly - agile methodologies are actually really bad at long term planning. Scrum, Kanban etc provide no framework for the long term. Lots of teams assume that this is because you don’t need to. You do. There’s nothing wrong with sketching out long term plans, roadmaps, and trying to plan for the future. Trying to think about making your product scalable, secure - you might not have to do it right away (and sometimes you just have to get something to show the investors!), but you should at least try to spot problems on the horizon.