I understand what they are saying but can’t they teach them to throw? Then once they know how it’s just a matter of practice. Seems like you could have a pile of grenade sized rocks at one side of a section. Throw them to the other side. Go to the other side. Throw them back.
That's pretty much what we did in BCT, except they were inert grenades. There was a 55 gallon drum at each end to lob them into. That became possible due to the ballistic trajectory of the throwing technique taught. When we had down time between scheduled training we squad leaders were to take our men out to the company grenade field to practice.
If we saw one of the trainees was weak in any skill, it was our job to bring them up to speed. This was in 1965, so always on our minds was many of us would be facing real war in a few months.