You obviously need Live Viewers with some engagement depending on ranking difficulty, but the main problem with live videos ( if your goal is to stay ranked after live ends ) is that you can rank pretty well while on live, stay ranked few hours after the live ends if the video did well on live, then the ranking drops suddenly after that if you dont achieve a snowball effect of views.
If your goal is to just rank while on live to gain subscribers, WatchTime, promote an offer, or whatever you want.... you will need to find a way to keep the live viewers watching your video. the viewers you see the fisrt few hours probably comes from youtube promoting your fresh live video, when they see that there is no to little engagement/retention, they will stop promoting it of course. you may not always benefit from this fresh live boost from youtube even if you make many successive short ones, as youtube sometimes takes into consideration your past performance.
The best thing you can do is make as many tests as possible to find what works best for you.
