Your point is that you need something fast and versatile for action shoots like kids, guitarists etc.
Well, i understand your point but if that's what you want to shoot, then the F4 isn't a good choice either. You could carry a Canon EOS 5, you will need no motor-drive, even the flash is built-in, and the AF is faster than the one in the F4. The EOS 5 weights 675g... not over 1kg. It even tracks the position of your eye. A later Nikon plastic-fantastic camera like the F100 would be a better proposition too.
Your main point is that you need quick response for action shooting. I would contend that nowadays this kind of action shooting is in the professional world already better, much better, covered by the plethora of digital cameras.
Personally the kind of photography I do doesn't need motor drives nor AF, thus I choose my cameras based on weight and the image quality that the format gives, using this criteria the ETRSi is a far better proposition than carrying a F4.
As for your claims that "you would need the grip, metering prism, multiple film backs", I don't get it. You don't need the grip to advance the film in the camera. Using the waist level finder is easier without the grip. And how would one need "multiple film backs" to "use it like a 35mm", when almost every 35mm camera out there does not support multiple film backs? Or you mean, "to reload film faster than a 35mm camera?" Because with multiple backs you can reload film faster than waiting for the camera to rewind your roll, putting the new one, etc.
Finally, i find your claim of ""goddamned guitarists and drummers are worse to photograph than unleashed puppies" strange. In the early 2000s i used to do concert photography with a medium format camera (TLR), and a 135 manual focus camera, a Canon A-1 It wasn't that hard. I guess everyone has different ways to approach such photography. There are techniques to cope, like pre-focusing, etc. And by the way, I play drums... we drummers don't abandon our drum stool, nor run around the stage like goddamed singers. I fail to understand how they would be harder to photograph than little children, which, YES, are a hard subject.
Yeah, you're being obtuse. Probably willfully.
In my specific example, they are young, wild, and the nature of the shoot was chaotic. I only mention it because, literally, I had an F4 and an ETRSi with me, but it was only an example. Other chaotic environments exist. For these kids, they wanted to do a specific thing in a specific way, and it was difficult and hectic. It was what we wanted it to be, though, to get the kinds of shots the band leader was looking for. You just have to accept that one.
Stage shots are way easier. Most musicians in general are way easier. Planned, posed shoots with these guys will be way easier. But then you risk nothing but "Jeremy standing in front of a brick wall" shots, and they don't want to be brick wallers.
Concert photography is way slower. MF works great for it if you have a fast enough lens or bright enough stage lights.
Chaotic environments are the bread and butter of 35mm. ETRSi is as good a MF as I've tried to shoot like I shoot 35mm, but it's just slower in all aspects. And if you don't understand why I'd need the accessories on an etr for walkin' around shots, well anyone who can shoot in portrait with a waist level finder is a better man than I, and shooting fast with the mirror locked down, wind wind wind (or crank crank on the grip) before you recompose... its as fast as MF gets, but it's slow.
I'm not going to switch to Canon when I have a crapload of Nikon lenses just because
you think I should save a little bit of weight, even though Canon made some really nice cameras. I have an F100, I use my F6 instead almost every time I want a "modern" film camera. I just don't care about weight if I'm not carrying the camera for a long time, so weight is NOT the point. My point is specifically that 35mm are NOT interchangeable with medium format, regardless of your personal priority for less weight. MF are more bulky, slower, less lens selection, narrower depth of field, etc. etc... they're wonderful in many ways. But they're not the same. None of these things are weight related.
And I'm not going to use digital for everything because the client very specifically approached me because I use film. They wanted film, period, and they paid for the film. Digital is technically better and significantly easier in almost all aspects to either 35mm or the ETR, and my camera is amazeballs. But that was not the job, and that camera is neither film nor 35mm, so not what we're talking about here.
Everyone has their own requirements. If you can't consider someone else valuing something you don't, or someone else encountering an environment different than one you experienced, that's just your lack of imagination. It's why "best" is an impossibly nebulous term for cameras, too. Everyone values features differently.