It depends on which Shrek your talking about. Giving Shreks to Pgrens unless you using Luftwaffe Supply, Close Air Support, or Oustruppen is always a bad idea because Pgrens are very easy to 1 shot and you need to stick them in the range of a tank to shoot the shreks. In that case a very large amount of micro is require to keep the Pgrens alive.
Volk shreks are easy to use by design since OKW doesn't have very plentiful and mobile AT (Volk shreks also cost a lot, with the income reduction accounted for they cost 112 munitions) because they lack of the fuel to get lots of Vehicles and the Rackten only has 50 range. If you opponent is spamming Volks you can do a couple of things:
1. Spam Harder; Volks have pathetic performance versus enemy infantry so get stuff like 1919 Rifles/Para's or Shocks which will tear them apart.
2. Crushing; this is a big thing because OKW lacks any kind of snare so he can't stop you from just crushing all his infantry without retreating. USF has the best vehicles for this but both the T34 variants can do it. Remember to make tight turns without stopping. And even if you don't crush them pushing Volks stops their shreks from firing meaning you can employ this tactic using non-heavy crush armor.
3. Artillery; Katyusha's and other artillery will annihilate Volks blobs, as well as blobs in general.
4. Kiting; Shreks have 35 range so you can kite them with basically any vehicle. This is best done with the USF AA HT since it also suppresses the infantry making them unable to move at top speed. With even better micro you can do with with duel MHC's and wipe squads like there's no tomorrow.
5. Overpower them; A good OKW player will volley fire his Shreks at 1 tank to kill it as fast as possible, a bad one will just let his shreks hit what ever. When facing a good player make sure to focus fire his Volk squads 1 at a time instead of shooting at different ones. Turn his tactics against him.
Or just employ none of those tactics and charge blindly into enemy lines with TD's meant to engage at range.
Yes those are all things I already employ and it is done much easier in 2v2, Allies period have it much easier in 2v2 and 1v1. It is when you get to 3's and 4's where you will get at least 2 sometimes 3 people with the grenblob or volkblob and just wait til heavys. If the shrek was not soo good at what it does then I do not think you would see the blobing you do now. It is pretty simple in most cases they really don't have to make anything else especially in 3v3 4v4.
as for the video yeah I would of split the tanks and moved them in a wider flank on each side. Why I posted it was if you noticed the ammount of dmg the shrek mobs were doing the whole time ultimately making a huge impact on how much dmg their late game vehicles took sometimes if your vehicle lives to take one more shot it can make a huge difference on which piece of armor survives (the king tiger). I probably would of used the e8 range smoke on top of the pak and shrek mobs.
Just saying why can't the shrek be on par with the zook. The shrek at zook levels would deal moderate damage and be able to ward off early game armor like the zook does everything up to pz4 but not be able to insta destroy a sherman e8 or 34/85 with one salvo (or very close to it depending). What if zooks were able to do that to panthers? I think that would be fun.