With a treaty,Manuel buys the necessary time to deal with the Balcans first and then organize a two-pronged offensive against Kilig Arslan converging on a certain place and entrapping his army;the same way that Omar was defeated in 863 AD by the converging thematic armies.Even with a treaty in hand with the Seljuk Sultan, Turkish raids on Byzantine territory will continue - a strong victory against the lot of them would really be the only thing that could stop them from continuing to attack the Empire.
It's not hard to see why Manuel wanted to win a major set piece battle against them.
The Seltzuks were not so strong.They were weakened by internal struggles and they were divided into many states,in some years their states were infiltrated and subdued from within;Byzantium had an extensive espionage system;they could easily find out that the Ottomans or Turks from Central Asia could be their future concern...The time period and location was one where a single individual leader or outcome of one battle was very important. Winning Myriocephalon simply postpones the point of decision by keeping the Byzantines able to launch strategic offensives. It doesn't guarantee they can keep winning.
The Seljuks were too powerful at this time to go away because of one battle. There is always the possibility that in some future battle they'll defeat the Byzantines and begin their decline again. Or maybe they won't, and the Byzantines keep winning.
However, a big enough victory might weaken the turks enough so that the combined strength of the Christian states (Byzantium, Armenia, Georgia, and Antioch/Crusader states) to keep Anatolia Christian. Or it might not. Things really depend on chance during this time so no one can say with any certainty what will happen a few decades after the POD.
The Seltzuks were not so strong.They were weakened by internal struggles and they were divided into many states,in some years their states were infiltrated and subdued from within;Byzantium had an extensive espionage system;they could easily find out that the Ottomans or Turks from Central Asia could be their future concern...
Many results?such as?They are strong enough so that the outcome still remains uncertain. All we can say is that region remains in play which could lead to the Byzantines reasserting their dominance, or losing the initiative again by losing the next big battle. Your scenario is certainly possible - I am not disagreeing - but neither is it the most likely scenario. Many different final results are equally plausible depending on what happens next.