For lighting characters, Infinity breaks the vast majority of LIs. Still probably in many instances it makes sense to use sunder charms as well or as a replacement to go with another merc combo. It is completely game changing on the other hand for fire and cold builds, because CI and FI monsters are often unbreakable.
I saw in the patch notes that at least they changed cold mastery to work at 20% effectiveness. Otherwise, Blizzard Sorc would have been ridiculous when combined with sunder charms. Now on the other hand, Blizzard Sorcs will almost be forced to use sunder charms. Not great either.
At least in some situations such as Trav Blizzy, which in 1.14 relied heavily on CM operating without the 1/5 penalty to bring down Toorc's cold resist after being broken by Infinity. This will now be a weaker Trav build, with or without sunder charms.
how about Infinity? Enigma? CtA, even? How about Hork? Or Teleport? Or Lightning Fury? Will an assassin with griffon's and crescent moon farm faster than a classic Javazon?
To me it seems you are mixing up a bunch of different things.
1) The game how it's been for 20 years: CtA, Enigma, you forget to mention Grief (which makes 95% of melee weapons obsolete). Yes it's all debatable whether these are too strong,
but that's been the status quo for the game for 20 years. Not going to debate whether these should be removed or changed or silly notions like that. That's the game as it stands, and touching that would be even worse.
2) Berserker/MF efficiency: Don't get me wrong, I didn't like Berserker buffs, but removing immunities is a much more extreme step which drastically alters core game mechanics. Barb's intrinsic power level did not become "stronger", he doesn't kill faster. He just became (even) more MF efficient. That's idiotic but not game-changing. And sadly, most people who really played at high efficiency around here are inactive nowadays. The Hall of Records thread is basically dead for the time being. For more casual players, the buffs make very little difference.
3) Sunder charms: The issue with sunder charms is completely unrelated to MF. In fact, I don't see sunder charms having any meaningful effect on the "MF power ranking" at all frankly. It will just be used to make strong builds even stronger, meaning increasing their killing power, which in my opinion is a shame.
You mentioned Lighting Fury, which I don't understand at all how that should support the argument? Because Lightning Fury is a prime example of why people think sunder charms are a terrible idea. Cookie cutter builds like this that already crush everything will become even stronger, and there's simply no reason to do so from a balancing perspective.
Instead, I believe the reason behind this is to allow people who do not want to spend the time to get Infinity etc. to be less limited with their build choices. But replacing a high-end runeword with a charm, and stronger in some ways (read: fire/cold builds) just turns the game upside down.
Next patch will perhaps be a grand charm "+1 to Teleport" with a 25% life penalty or something... then I would really stop touching D2R.
Anyway, my 2c and that's all I say on the topic...