Also in response to "Grenadiers will beat Riflemen at long range" I've decided to test it. Squad vs Squad controlled test, long range, no cover, no vet, no outside factors, no retreating, 20 attempts. Grenadiers won 9 times and Riflemen won 11 times.
The number of survivors per-lane is as follows:
Surviving Grenadiers: 3 2 2 2 2 1 1 1 1
Surviving Riflemen: 4 3 3 2 2 2 2 2 1 1 1
In other words, with both sides on equal footing, victory is mostly RNG. You may take one casualty or lose the squad and anything in between. Riflemen seem to have a very slight statistical advantage, but they have a completely advantage in any sort of actual fight unless Grenadiers are caught in heavy cover and force Rifles to charge. But of course Grens in heavy cover aren't out capping, and heavy cover isn't always available nor can they create it.
They can however make building cover.