The only change/buff ermac could really use is having the "1" in the 312 string jail the opponent or make f4 on its own safe.
As it currently stands, most players will just block all of ermacs block strings and react accordingly.
Block strings such as b114 , 121 and f4b2. F4 can also be punished if used on its own. It would be amazing if it was safe like U4.
Now as for the "1" in 312 jailing the opponent. Currently this string is ermacs best string. It is cancelable and allows for mixups. A lot of ermac's pressure can come off this block string. IF you want to see how this is best to be used please watch videos of Krazyie Bones ermac, as he is the only other ermac that I see using this effectively.
Now after the "3" hits, the 1 can be interrupted by a fast uppercut or a low poke.
If they just changed the "1" to be able to hit the opponent if they so choose to stop blocking, I think this would be really all the fixing he could use. As it stands it is really not hard to stop this string and halt ermacs pressure.
If f4 was made safe, this would make his upclose pressure more viable as well.