The Sherman isnt so much a shock unit anymore, but its ideal for attrition (like the Scott), especially if you reach a critical mass,
The thing is I don't like playing an attrition battle. I am more of a shock and awe type. My personal strength is early game. Good micro and tactics with a managable number of units. During mid and late game I loose efficiency.
This is why I like to use shock tactics and end the game in 10-15 minutes. Because I know my time is running out and the longer it takes the more stressfull its going to be and my chances dwindle.
As for COH, the M20 pretty much serves the same role against Ost as the M8 used to do against Wehr back then. Its actually easier, since you are almost guaranteed to have the M20 on the field before he can get a Pak or 222 out, and once he sees LT tech the Ost player virtually has to use T2 or he will get rolled, while in COH you could always call in the emergency storms and go straight for T3. On the flipside, the impact of the M20 is indeed less than the M8 had. That .50 cal was just brutal...
The M20 might be supposed to fill the same role but like you say in your last sentence it isn't up to it. The fact that the Faust of the T1 basic inf is a snare and that Schrecks can snipe it prevents it from doing so. The M20 simply lacks punch and survivability.
In CoH1 the Stormtrooper were no real counter against M8. They were doctrinal and 3 CP. Its not a given they would be there if the first M8 hits the field. Even if, the Schreck was way to inaccurate. Of the two shots one would usually miss a moving M8. This gave it time to rush in and force a retreat because killing a M8 with upgraded skirts would need at least four hits. Trying with a four man Storm squad would be a gamble.
In CoH1 1v1 T2 was more or less a no brainer for WH. T1+T3 could work but it dependet on lots of things. T1+T2 was the safe bet. Actually T2 was all you needed. T3 and T4 were fully optional if you had T2.
T1+T3 strat was based on having a strong T1 map presents and prevent the US from getting enough fuel to rush M8 faster than Storms and Pumas were available. It also relied on mines etc. It was not like "oh he has an M8 i call in Stroms, upgrade them and M8 begone!" In the time it took to move the Storms to the front and upgrade them wich, was quite expensive munitions wise, the first M8 most likely would have cause conciderable damage possible even force a mass retreat and a second one would be about to hit the field.
The hard counter for an M8 was the Pak and even if you had one a single M8 would overpower a unsupported Pak every time. It would take on hit guranteed and maybe a second but then it would circle strafe the Pak to death. Try to rush and circle strafe a unsupported Pak in CoH2... even a Vet1 MG42 and shoot the M20 up. A single Gren squad can assure its doom by fausting. Seriously I fail to see any shock value in this unit. The M20 is intresting for harrasing and counter harrasing. Kübel hunting and an early Bazooka but rushing it and building a second and third as quickly as possible will hardly win you the game.
At least it won't with my skill.