Yeah, I personally find using separate AWS accounts for dev/test/stage to be a bit of a PITA overall, prefer to isolate those resources via VPCs & IAM policies in an umbrella non-prod account, but definitely see how that would simplify other aspects of setup.
The path limit isn't a huge issue, just something you have to design around up front. As you mentioned in another comment, no reason you can't store a JSON or something in the string if you need deeper nesting.
For secrets needing to be shared between teams I'd just create a different prefix in the place of team, like /shared/, and grant access appropriately. Or just use no team prefix at all and make it accessible if it's for everyone.
But it's quite nice that the service is flexible enough to be useful for a variety of use cases / infrastructure setups.