Whats with all the fuss?
UsF AA HT always came early and has essentially the same effect as the m5. (if we ignore reinforcement)
Counter the m5 the same way you have countered the m15 for a year.
There are very significant differences between the M15 and the Quad M5. If there weren't any, this topic wouldn't have existed because like you said, you could have countered it the same way we have been doing for the past year.
One of the differences is that the M5 quad can deal with 222s and supress infantry excellently while one the move. It can also reinforce which is a huge advantage that you can't just ignore.
But more importantly than all this, is the fact that the Americans are a completely different faction than the Soviets. Let me explain. First, lets look at the Americans. You can turtle defend just fine against the M15 with PAK40s. The reason why this is pretty balanced and has not been a major problem for the last year is not about the M15, but about the possible follow-ups. The Americans can not follow up with both good AT and good indirect fire options. If they followed up with Shermans, the Pak40s could hold the line, if they followed up with a Scott to deal with the Pak40s, they were left vulnerable to P4s because they had no AT. The winner is decided by good risk-assessment and tactics.
Now look at the Soviets, what do they have as a follow up? Good indirect fire and plenty of AT. They don't have the weakness of the Americans that can be exploited. They can follow up with an AT gun and SU76s to remove and shock value of the P4 while
at the same time providing the soviets with the required indirect fire to deal with the Pak40 wall.
In 2v2s with 2x sovs vs 2x Ost, the soviets can both get out a M5 quads at the 7 minute mark, dominate the map, and follow up with a either mix of T3 and T4 units (one goes SU76 spam, the other goes T4 for katy and SU85), or just SU76s, supported with 1 or 2 AT guns and from there on out it's a very quick loss for the Ostheer. Once they have their double P4s out (both have to go T3 as T4 is so expensive it is out of the question) there is enough Soviet AT out on the field to remove the shock value these units would have had when playing against the Americans.
That if the difference between the Quad M5 and the M15.