This is somewhat of a tautology: if your architecture was good then it still is. But it is hard to define "good" or "well designed" or "better than that other

This is somewhat of a tautology: if your architecture was good then it still is. But it is hard to define "good" or "well designed" or "better than that other one". A slightly different take: there are a couple of categories for system changes: (a) adaptive changes to respond to a changing environment or requests for new functions, and (b) corrective changes which fix bugs (bugs of any age). Examining a proposed architecture with these two categories in mind might help. As long as changes are correctly categorized and therefore the scope of changes matches, your architecture may be seen as better or worse. Or more or less survivable. And on yet a completely different perspective: choose between two or three possible architectures. If you haven't got a choice then you need to fix that.