I am not an expert on this things but in my opinion when we talk about codes there are several things to consider. The reason why core developer does not accept Bitcoin Unlimited its because it runs on hard fork and it is going away from the original form of bitcoin. Bitcoin Unlimited does not want to accept Segwit since they dont see the code fit to run and replace the current code.
I guess it is not about code or technics. It is about power and money.
The obvious difficulties bitcoin has with too many transactions are a welcome argument for brutal measures -- with subsequent accumulation of power. You know, "populism"...