Grens with mortar and MG support can definitely hold their own against infantry sections, and with some clever play you can defeat a Rifleman force too (example: 3 rifles smoke an mg, close in, get into close comabt with Pgrens with a predictable result).
Also note that Pgrens are not meant for frontline engagements. They are flanking troops that do really well at medium range. Think of them as more durable Fallschirmjagers (which are hardly defenseless against Allied infantry) that are worse at long range but the same at mid and close, and use them as such.
In the late game you can't.You can hold back once or twice,but eventually they will break through.Mgs are less and less effective as vetted infantry dodge bullets.The scenario ur talking about works in early and mid game max.In lategame after smoke rifles getting close will still overwhelm pzgrenadiers due to ridiculous vet and 5 men.
What you are essentially saying that axis infantry requires perfect micro and luck against just plain frontal blob attack of allied infantry EVERYTIME every engagement lategame just to defend themselves and prevent themselves from being wiped out,forget any basis of competitiveness which only proves my point.