The Teef system is supposed to be limiting, and that's kind of the point, really. Progression isn't supposed to be mega, some crews are going to be crippled by circumstance and never recover etc. This is part of the fun of SGs. There isn't a buffer zone to keep things about level, like there is in Necro, but there's also less likelihood of Mobs zooming away in quality, especially if all players know what they're doing.
Anything can happen, and that's an idea that is not old-fashioned, it's the hallmark of good design.
And ultimately, if you want to change the game for a different experience, why not just make a whole new game? 40k is just not a good system for "breathing life" into SGs. A crisper, more refined version of the old 40k Skirmish System is better found in the LOTR/Hobbit ruleset than 40k. 40k just isn't very good, and it just doesn't work for a skirmish. The rolling is too forgiving, movement is too generous, cover saves are pretty meaningless because the firer is rewarded for taking any kind of shot regardless of difficulty, and the majority of the rules are either clunky gimmicks, or streamlined for brainless simplicity, which is fine when you have 100 models to move. Doesn't fucking matter when you're moving 2-15.
I imagine combat will just be a stupid mess, often with mutually wounded, hobbling models that couldn't take each other out. If they wanted to speed up the game, they failed right here. With the old 40k Skirmish system, a model taken down is taken out straight away. That just doesn't work if your melee isn't broken down to a sort of duel system, and it just becomes a case of roll 6s on the right kind of roll: the game. Well done guys.
Oh and on the frequency of this chopping and changing in RP circles, the fact is, RP is about Role Play. It's players engaging in a story via a GM. A ruleset is just there to help the GM sort stuff out, and in many cases when I GM, I don't consult the rules for very much. Whereas miniatures games are not like this. Systems are far more important, and the overall feel of how each game is played varies, and there are no GMs (usually) to regulate how the game aught be played. Taking a large scale battle game written by morons and attaching onto a small scale finesse skirmish (thus removing much of said finesse) written by GW when they had writers with talent is idiotic from any perspective.
40k doesn't really modernise SGs, and pretty much all of them have nothing to do with their foster systems. It would be like trying to crowbar Warmaster into using the AoS system "because it's modern". It makes no sense whatsoever for that system.
I still don't get why they've done this. But as they think adding the experience of 7th Ed 40k to anything as a good idea, I think they do deserve the bad results they're experiencing.