by my experience you should not post shorts on main channel , I used to manage a channel for my friend and he did gaming live streaming , and got 40K subscribers , and he tried to make shorts on main channel and after a month or so his live watch dramatically decreased. His channel was audience targeted , after uploading shorts his audience becomes unknown language speaking people (analytics say so). and his channel never recovered from that problem , now he stopped shorts videos and starting from zero again ,, last year when he live , he used to get 50-60 constant watching ,, now its 5-10 only,
I hear you - mixing shorts, long-form content AND live sessions can be confusing to dissect which or what caused for it to decline like that. Then again, if one remains within their niche, YT algo's should pick that up. I have to see major research or studies done to indicate that it's hurtful to have all of the above on one single channel.
Whilst I definitely don't know what happened with your friend's account, I'm cognisant that social media platfoms shift their focus around (ie pushing more traffic towards certain new products or new direction, hereby taking eyeballs away from something else -- ie upping shorts & reducing number of live sessions?)
I haven't done a single YT live session, BUT I can only imagine it'll be similar to Instagram where I have quite some personal experience with live video...given I have 260,000 IG followers, I used to get 2,500-3,500 people on a single live session about a year ago...that's now down to 1,500-ish. Organic reach being squeezed?
Please find below a screenshot of my 28-day YT activity from my shorts alone - mind you, I don't have any shorts that go viral, all except for a couple are lower 1,000's and I'm posting a new shorts video every 2-3 days (I'd like to up to that daily given these recent results - especially new subscribers!)
My 2 cents.