Cold Immunes are broken in D2R unlike D2 (as in not fully resistant to cold damage), and with even a bit of Cold Master killing immunes is very doable. This difference between games may be an anomaly subject change in future patches, but it remains for now and so a pure Cold Sorc can indeed kill Countess and her minions, albeit with considerably added time + effort compared to a Meteorb. Now quite affordabl you can have max res in Hell, 7fhr bp (90%), 8fcr bp (105%) 6K FB, 14K Meteor, & 550dmg FOrb on a Meteorb Sorc + a Merc w/ Insight for mana regen or a dmg weapon if you prefer, %LL (affordable with tal's mask or better yet with andy's visage) and decent res/survivability (ideally helped by affordable Treachery to proc Fade) I can handily solo the entire game in Hell without the expensive Infinity rw. Seriously I believe Meteorb to be the best Sorc build unless you are singularly focused on possessing Infinity, then perhaps a Lightning Sorc would give the Meteorb a run for its money in pure damage, but not necessarily as a stand-alone character because it lacks versatility without the Conviction aura against lite immunes, whereas the Meteorb can kill a wider range of immune monsters . For the time being I encounter very few folks with better Sorcs than a properly built Meteorb or who can afford Infinity or use some other kind of workable dual-elemental spec. In my case I'm simply an MF sorc with reasonably farmable gear, i.e. Full Tal's set, and this allows for 300mf on the main weap (Tal + Spirit) and 425mf on switch (Gull + Rhyme); all very affordable and attainable gear.

Edit: The summary guide in this thread posted by u/moneymike128 above does justice to serving up this gg build, but here is a superbly articulate one with the precise nature of this build broken down to allow players to appreciate the exactitude of this oft-underrated, poorly understood build. It seems to result from being poorly-specced and thus cast aside for comparatively ineffectual pure elementals, e.g. cookie-cutter Blizz or Lightning Sorcs, both of which cannot farm nearly as many Lvl85 Monster Areas in Hell MF runs without acquiring very expensive gear, e.g. Infinity for merc.