> So for me, this usually precluded any full-frame system, unless you wanted to use F4-8.0 glass
Gosh where to start!
1) not necessarily. I travel with an R5, 50/1.8 and 16/2.8. I can crop if I need to but I'm used to moving around to shoot 50 anyway. These aren't "f/4-f/8".
2) You say f/4-f/8 like its disreputable.
In the 90s, we needed an f/2.8 trinity just to get the AF to work well, so it was non-negotiable no matter what you were shooting. But even 100-speed film looked worse than ISO4000 does today, so in anything less than broad daylight you were fighting between worsening your photo with higher-speed film yet, or longer shutters that worsen with hand-shake or subject movement. So an f/2.8 lens gave you a third option of opening up. Now, autofocus was frankly crap and especially at f/2.8. If your subject was centered you could use a split-circle to focus a perfectly centered subject, boring. Or you could focus-recompose-shoot but since the "plane of focus" was never a perfect sphere, when you recomposed you were no longer in focus. And even if you got the eyes in focus, the rest of the portrait wasn't in focus at f/2.8. Given the losing war on focus, AND the grain, we didn't use huge enlargements. In a small image we still wanted the subject to pop, so f/2.8 gave us that at least. In a 10x15cm/4x6" print, the bokeh from f/2.8 would let you know what the subject was supposed to be.
But now things are different. We can shoot four-digit ISOs all day long and have usable images. AF nails the focus now, especially with eye detection and eye-AF (eye-directed AF), no matter how flat or curved the plane of focus is. IS and IBIS mean hand-shake at least is a thing of the past with even the 50/1.8 reliably shooting at 1/2 sec. Our grain-free, perfectly in-focus images are ALL previewed on 19" monitors or bigger. And at that huge magnification... f/4 bokeh scaled up to monitor-size is far more notable than f/2.8 bokeh is on a 10x15cm/4x6" print. And f/2.8 doesn't buy you anything with AF either.
I would submit that the trinity zooms of today are the f/4 series. Due to images being fair multiples of size larger than the film era, f/4 is plenty. By all means get more aperture if you want, but it's hard to say it's necessary in the same way it was necessary in the 90s or 00s. Some may really want or need EXTRA bokeh and use the f/2.8. (Extra--due to the fact we look at photos far larger now, not because f/2.8 today is different than f/2.8 in the 90s.) But I suspect a lot of people do NOT actually need the f/2.8 and are using it because that's what they've always used, or that's what the common wisdom says.
(BTW I get big apertures. I've owned the 50/1.0, 50/1.2, 85/1.2, 135/2, 135/1.8, 70-200/2.8, on up to 600/4, and I'm the one who posts about how Canon should make a 35/1.0 and 50/0.7 as halo lenses. I'm just saying these are for special shots, but they're not needed like they were 1-3 decades ago.)
3) You say f/4-f/8 as if the APSC lenses can be compared like-for-like with full-frame because the f-stops are somehow comperable.
The f-stop isn't actually the aperture. It's the focal length DIVIDED by the aperture, and the aperture is the hole in the front the light goes through. Aperture is where bokeh comes from. an 85/1.2 and 135/2 and 200/2.8 and 300/4 and 400/5.6 all have about a 72mm aperture and they're produce the same amount of bokeh. The photo is wider or narrower of course, but take the center of a wide-open 85/1.2 shot and it will look nearly exactly like any of those other lenses wide-open, neither more nor less bokeh. APERTURE is what you want to compare, not f-stops. In fact an EF50/1.0L only has a 50mm aperture, and doesn't have near the bokeh of the series I mentioned.
So if you're using an EF-M 22/2 and saying, gosh, the multiplier is 1.6x so it's comperable to like a 35/2 on a full-frame sensor, it's not. Well: for exposure, yes, but not for bokeh. That hole on the lens doesn't magically get bigger. If it's equivalent to a 35mm, 1.6x longer, then the f-stop wide open is 2*1.6=3.2 wide open. If you haven't shot a lot of 35mm lenses (and I haven't) like 50mm f/4.5 levels of bokeh, when you have it wide open. Not much bokeh.
And if you're using a kit zoom, actually, ANY zoom on the M, it's bokeh suffers the same fate. A EF24-105/4 on an adapter on an M might be like 40-160mm, but while it still exposes like f/4, it bokeh's like 4*1.6=f/6.4.
So even the EF-M primes are only a pinch more bokeh than full-frame f/4 zooms in many cases, and the APS-C zooms generally aren't comparable at all.
Finally, the only time you're really talking f/8 on a full-frame Canon is really crazy focal lengths. The 100-500/4.5-7.1 is getting pretty close to f/8, but it's not there yet, and it's only even f/7.1 at some pretty hellacious focal lengths. And again, it's aperture at that point is 500/7.1=71mm or so... so it's actually bokeh city, as much bokeh as an 85/1.2 or 135/2 or... It's unreasonable to scoff at the idea of f/8, when that f/8 is at 500mm (and actually only f/7.1, too.)
4) Yeah, weight and size restrictions are draconian but the R5+50/1.8+16/2.8 doesn't weigh much. And you can always smuggle it in in your armpit, as the chubby Americans would riot at the prospect of airlines actually weighing the PASSENGER :-D
5) as much as I enjoyed shooting my EOS M (I randomly passed through Bic Camera the day they went on sale and picked one up) within two years I had switched back to the 1Ds MkIII and even the old 50/1.8MkI if nothing else. I didn't want to manage two workflows and wanted to keep the muscle memory working on just that one body. And the M wasn't built well enough that I thought it could even survive life in my backpack, whereas I only ever worried about the 1Ds breaking OTHER things...
Anyway, these are just my thoughts and the above all general observations. I know there will be some exceptions and maybe I'm flat-out wrong on a point or two. Show me an APS-C photo with more bokeh than you could get with a stripped-down MILFF, or whatever counterexample you have and I'll be happy to eat my words. Bon apetit.
