"Failed design" is a bit harsh. It had a relatively short time in service as the biggest, bestest ship ever, yes. But that's just as likely a symptom of it being from an era of rapid technological changes rather than fault with the design itself (both in and out of universe, amusingly enough).
From that same thread:
And as shown by Picard season 2, while the GCS and Sovereign were quickly outdated, they're still in service with the fleet, just longer the latest and greatest designs.
From that same thread:
Consitution: 2244-2285 (41 years)
Excelsior: 2285-2325 (40 years)
Ambassador: 2325-2357 (32 years)
Galaxy: 2357-2370 (13 years)
Sovereign: 2370-2380 (10 years)
Oddessy: 2380-2410s (30 years and counting)
And as shown by Picard season 2, while the GCS and Sovereign were quickly outdated, they're still in service with the fleet, just longer the latest and greatest designs.