Grenadiers seem to get instagibbed quite often. While they CAN be good at range and with LMG (and must remain stationary) they just seem to be outclassed and die like flies. Really their survival rate is just atrocious. I never have to babysit infantry units like I do Grenadiers. Because down to three they have your attention, two is instant retreat, and one...well they're basically dead. (Usually.)
Panzergrenadiers seem to be a lot tougher, even with the higher cost but don't die as often and scale better. Infantry sections, Riflemen, and now Penals beat them down pretty hard and almost every encounter for several reasons.
Toss in the fact of how often scout cars can chase down Grenadier squads quite early because they are symbiotic in use with flame engineers/scout car. Really Tier 1 is almost pointless against Soviets because you're needing a Scout Car to deal with Stuarts/Scout Cars/(Random cheesy early Allied unit) because it's all you have. Tier 1 is just pretty bad against Soviets in general. There are too many Russians for snipers to be effective, mortars are a liability with scout cars running around and Grenadiers die faster than Sean Bean.
That's a little off-topic but Grenadiers are kind of like Sean Bean. You know their fate before they even meet it. Virtually walking spoilers.