Not to mention the logistics. Chapters rarely have the logistics to send ships on missions with only a single Marine. They might have lone marines in charge of largely "in control" locations, where they act a a governer of existing infrastructure and military strategy, where they are an advisor to the military operations; similar to how they worked in Salvations Reach; 3 Astartes aid with a battle plan.
If you consider that each one is armed with an .75 calibre (18+mm size round, the equivalent of what comes out of a AH1Z Viper; essentially 2m "you are dead in here" zone, and a 20m frag radius) rifle with rapid fire capabilities, but also, presumably, due to its rocket assisted munitions, and the additions of an M.40 Targeter and Silencer, the ability to transform into an effective Anti-Material rifle; it wouldn't surprise me to learn of a Bolt round with small stabilising fins, which enable it to correct its course in flight.
So, if you want allegories, and to compare weapons systems; an AH1Z would be equipped with a S4 AP5 weapon as its main chin turret (although possibly of higher rate of fire).
A Rotor Cannon from the Heresy is a Marine portable heavy weapon; so likely a vehicle mounted equivalent would be an M134 (7.62 Gatling, rather than 20mm); are S3 AP6 Salvo 3/4.
As this is possibly the nearest we have in terms of weaponry to what 40K has, Salvo 3/4 represents a weapon capable of spewing out between 2000-6000rpm, S3 represents 7.62 ammunition (non explosive) with a muzzle velocity of 2800 m/s, and 30" range represents a km of maximum range (or possibly half that for maximum effective range).
Consider how quick that would chew through soft skinned targets in today, and even lightly armoured vehicles like Wombats or Humvees. That's probably AV9 for a Humvee. Not to mention how quick it would go through a human, body armour or no.
The Imperial Guard have Flak Armour which provides an Armour Save of 5+. That means that their armour has a chance of withstanding hits from what is considered one of the biggest levellers in todays armed forces; an M134 Minigun that is so heavy it cannot be adequately carried unless on a vehicle.
Yes, this is combining fluff and rules, and catgirls are dying left right and centre, but that's using the information to hand.