When fighting against other infantry survivability depends on the ability to handicap enemy dps capabilities. We can create any situation and engagement against infantry and we'll see how having a single model with an mg42 allows mg42 grenadoers to be better because that mg retains its dps, so that survivability is just apparent as damage is dealt and entities drop. This is why squads that have a dps distribution that is more even between all squad members are less elite and generally cost less to reinforce. VSL is not a bolster infantry where you simply add a squad member. You trade that better dps upgrade with the extra squad member, but the squad itself will always perform worse in any situation, so there's no use for that survivability. This may be my opinion and probably it's not popular, but the overall value of the squad goes down, and so should the cost to reinforce it. The moment VSL drop 2 models their dps is greatly impacted, while this is far from true for lmg grenadiers, and dps retention causes the enemy to drop models himself, meaning it will be able to deal less damage overtime than it would while fighting with VSL grens
Playing devil's advocate here; while I agree with your point about LMG grenadiers having an advantage in battles because of DPS output, I definitely can't agree that LMG grens are more durable. Yes, LMG grens will drop troops faster than VSL grens and therefore take less damage overall, however I definitely think that 5 men is nothing to sneeze at. Especially with the free medkits. If you properly support VSL grens you can repel enemy attacks and heal for free, which helps to offset the lower DPS because you have an advantage on model health IMO. I definitely think that it's a poor choice offense-wise. But then again, if you want better offense you have panzergrenadiers.
Honestly I think it's very useful to have a more durable snaring squad to support tanks, even if it's not incredibly effective at dishing out damage.