I did not say Janissaries existed first in 1444. I said they were determinal first in battle of Varna(1444).
I know their cavalry were numerically superior to janissaries but that doesnt change the fact janissaries were the core of the army.
The entire army was centered around janissaries. The typical war plan was janissaries were on the center, sipahi and akinji etc would engage enemy then retreat behind center and at the center janissaries would volley fire along with cannons and that would destroy the enemy. Everyone else was just a distraction, it was the janissaries that did the job. Ilber Ortayli confirms this.
They did this tactic in Varna, in Otlukbeli, in Chaldiran and in Mohacs and all the other battles of Ottoman classical period.
For the sieges janissaries were even more significant. First azabs would attack, then dismounted sipahi and with these the enemy would be tired then janissaries would attack. They would be the ones expected to capture the city.