I dont know what all the fuss is over high ISO. We rarely even go as high as 800, let alone 3200+.
Fast glass and better camera holding techniques for slower shutter speeds trump high ISO any day.
What did the pros do before digital cameras could handle ISO 3200?
I can tell you what the pros did.... we didn't take the shot.
When we did weddings, we went up the choir loft looking down over the church during the ceremony and took a few shots with the camera either on a tripod or resting on a rail so that we could take a long exposure shot. We couldn't get close. We couldn't take sorts of shots people expect today - while the wedding was actually happening.
When you see the old shots of rings being exchanged, etc... we faked those. After the wedding was over and we did the "formals" at the altar, we asked the officiant to remain for a few shots and we re-created those shots... but with lighting because ISO wasn't an option. That was normal. TODAY, a good body and a quality 70-200 f/2.8 lens will let you take the real shot. Sometimes the real shot isn't as good as the fake as we can't control someone standing in the way (I've had weddings where a bridesmaid or groomsman blocked the shot - I'll move around considerably to get a good angle, but it's not _always_ possible.)
This is really a problem "during" the ceremony. You cannot use flash photography during the ceremony. Afterwards... flash away! Just about every shot before and after the wedding as well as reception shots (including outdoor daytime shots) are shot using flash.
I can go through some weddings I've done and find the ceremony shots and a typical exposure might be ISO 3200, f/2.8, 1/50th sec. In a _very_ well lit church I might get to drop the ISO to 800, but needing to shoot at 1600 or 3200 is common.
I do have a lot of concert event shots where I can't use flash and I will occasionally need to shoot at 6400. Not because I want some really high shutter speed... I'm often shooting at 1/60th or even 1/30th.
most churches we have shot in have been fine with flash photography.
the very few that don't allow it have been reasonably well lit enough that f/2.8 glass and ISO 800-1600 were enough.
plus, a lot of those churches that didn't allow flashes were more than willing to turn all the lights on for the wedding.
I don't know about "the good old days", but in the last 5-6 years, the churches we have dealt with for weddings have been very reasonable to our lighting requests, and some of them have even gone out of their way to get all the lights turned on and at their brightest just so the area could be as well lit as possible.
all our zooms are f/2.8, and if that wont quite cut it, we have a bag full of prime lenses. we still have to recreate the occasional shot, but not very often. I can definitely see your point as far as low lit venues go, but a lot of churches nowadays seem to be fairly well lit.
but hell, we're still in the equipment dark ages...nikkor D lenses... no VR, no nano coating...they seem to work though.
we don't shoot sports or concerts so i don't have much to say on those.