The main issue is around equity.
15 minute cities work great for high-paid knowledge workers with flexible schedules who can chose how and where they can work (i.e. laptop + wifi). But this is not true for everyone - you cannot expect everyone to find employment within 15 minutes of their home (e.g. healthcare workers, factory workers, maintenance workers, etc etc are unlikely to e.g. find a factory within 15 mins of their house).
Making area support more active-transport (i.e. removing road space and replacing it with pedestrian and cycling space) also has the beneficial side-effect of making it nicer for people and thus more desirable. So property value and rents go up. And again, the high-paid knowledge workers and their families are fine, but the poorer and less well paid are priced out. The lower-income families have to move further out into lower-density areas where there is not enough density of population to support smaller grocery shops, pharmacies, etc so the 15 minute rule stops working and now they need to pay to run a car. And where you do retain roads for the essential transport needs (e.g. grocery deliveries, emergency services, garbage collection etc) you end up with the lower-income families living there since they are less desirable and cheaper and it is those who suffer from that the most (pollution, noise, safety etc)
If you remove roads of block access or removing parking etc to promote active-transport you also disproportionately impact those with accessibility problems. Not just "disabled people in wheelchairs" but also people who are not officially disabled but would benefit from driving, e.g. pregnant people, or elderly people who are fine but cannot walk distances regularly etc. 15 minute cities punish people who cannot easily walk or cycle unaided.
Basically the "15 Minute City" idea is only for rich white-collar knowledge workers. It forces lower-income families and workers out of a neighborhood. I am undecided on if this is "working as intended" or not.
It seems like the solution would be making nice cities less rare, and thus less of a hot commodity, rather than preventing them. After all, nearly anything that would make an area nicer to live in, would also make it more desirable, and therefore less affordable. I can't believe letting inner cities be hideous slums is the best thing for society overall (historically, indeed quite common).
You can't have the entire place be 15 minutes because some people have jobs etc that are just incompatible with that, and they tend to be lower income people.
One popular way of talking about building for people is the concept of a "fifteen-minute city": neighborhoods where you can get to your daily needs in that much time by walking or biking. This does not require super-towers or any unusual level of density. My own neighborhood, about ten years older than yours, comes very close, and while it has some apartment buildings, none are taller than half a dozen stories, and there are just as many people living in townhouses or single-family homes as there are in the apartments.