The KMT was morally abhorrent and politically inept. They were so bad that popular support and sentiment in the United States was actually in favor of Mao.
They were so militarily weak that our Congress openly discussed how sending them any aid was completely pointless. How despite already giving millions in aid, it was just squandered.
Towards the end, they literally kidnapped peasants, handed them an American supplied gun and put them on the front lines without training them how to even shoot. This literally happened. With the very unsurprising result of a bunch of well armed peasants who are very angry for being kidnapped and don't even know how to use their weapons do not fire upon the communist soldiers but rather join them when they arrive, furnishing Mao with a very motivated soldier who is extremely well armed.
You can actually read transcripts of US congressman talking about how pointless it is to aid the KMT because they were so inept they literally didn't even train their soldiers how to fire the rifle. There are anecdotes of soldiers not even sure how they should hold the rifle.
Let's say you remove the communists from the picture, well then you can't do so without removing the KMT as well. You see, both were very marginal forces until the Soviet Union came about and helped them build Whampoa Military Academy where they trained and built an army to march North and piece by piece end the warlord era.
The Comintern didn't feel the CCP was mainstream or strong enough yet to militarily support so they lent their expertise and funding to another group with a better foundation under the condition that they ally with the CCP.
The Comintern all along planned upon using the KMT to grab power then gradually replace them with the CCP. The KMT saw how this would occur and acted first, rounding up and executing all the Communists they could.
It's called the Shanghai Massacre
To put this in perspective, this is no different than if the Democrats figured they'd be better off just rounding up and killing all the Republicans.
The surviving remnants went underground and the civil war was about to begin. The KMT made a crucial error. They were unaware of just how deeply infiltrated they had become. Many sleeper agents were placed in the KMT who were never exposed and this would be disastrous in the upcoming war. You really can't win a war when dozens of your top ranking people are actively feeding information to the enemy.
The KMT were in essence setup to fail. They were always upon an artificial platform never really earning their place but rather being sole recipient of massive amounts of foreign aid to help them coerce the other warlords to swear loyalty.
Nor did they ever truly control China. Those former warlord territories were still very much like independent countries. They were still under the same warlords who just now paid lip service KMT. In essence, very little had changed and the amount of territory under actual KMT control was quite small. This is easily demonstrated by the decision to not put up much of a fight but rather consolidate control elsewhere when Japan annexed Manchuria.
So even if the KMT somehow fully wiped out the CCP in 1927 it's very doubtful they'd have lasted in power much longer. It would have simply been a continuation of the warlord era until some other faction arose and settled the matter. They'd just be on another long list of historical footnotes.
Can you name the other groups or people who led China in the 15 years between the fall of Qing and the Northern Expedition? They'd likely just get lumped in with those anonymous people as yet another ephemeral group eventually replaced by the ultimate winner.