I was buying new pedals recently anyway so was looking into it before this threadTo be honest it never occured to me to look at Lifestyle YouTubers for studies. Not sure why you would.

Apparently most of the power comes from the down pedal not the uplift and any performance increased was balanced by the increase in expenditure of energy.
A cyclist could swerve or fall for any reason.
That's why you them a wide berth and can be fined for not doing so. It's that simple.
Re cleats:
It's not just about efficiency in the sense of power output against an optimally placed foot under different loads and you don't need to be a competition cyclist to benefit. With cleats properly setup, control of the bike is better, your feet will likely never slip out, your body will never have to continually micro adjust the feet constantly, you will move about on the saddle less, the pedaling stroke will be better and likely more symmetrical, the pelvis is likely to be more symmetrical on the saddle itself and so on.
If you cycle regularly as a more serious hobby the symmetry part is vitally important as most people don't walk nor pedal symmetrically, even with cleats. This will lead to problems at some point depending on your hours on the bike, it's literally a question of time spent. Knee, feet, hips, and of course, your backside.

and I did say in one of my original posts if you are a serious road biker doing large distances with hardly any stop/starts then cleats are the way.
I can think of one time when cleats were vey advantageous, my left pedal arm fell off and I couldn't get it back on and I was able to cycle the 2 miles with one foot![]()
you can really injure yourself - normally the knee goes first.

What caused it?
Driving and riding standards have massively declined.
Cyclists are unaware of the Highway Code, I rarely see arm signals nowadays. In London, they jump red lights all the time.