However, I do believe a (slightly) better competitor could be created, with better technology, better workflow, etc. If well-capitalized. If it had well-factored plugins. If you had a top-notch team to design all that and then build it.

That's a lot of ifs. Joel says it isn't guaranteed a brand new team will even do better than the old on the essential angle. It's risky and costly enough to prevent it from happening.