If you are shooting an IBO weight arrow (350grns) at 70lbs draw, an IBO weight arrow at 80lbs (400grns) will leave the bow at almost the same speed. Any chronograph owners want to check that statement feel free to do so.
It's true the higher poundage set up will have more K.E. but the increase in speed, if any, is likely to be marginal. This is because the arrows shot from heavy weight bows MUST be heavier.
The only real reason to increase draw weight substantially is to get more force available for the distance of penetration you would like to achieve. In other words more Kinetic Energy. By definition that is exactly what Kinetic Energy is, the potential for a projectile to produce a certain force over a given distance. Momentum limits how much force a projectile can give up in a fixed period of time. Kinetic energy limits how far the projectile may go when exposed to a specific resistive force.
In Africa, a 70lb draw weight is considered absolutely adequate for Kudu sized game (about the same size as elk). Unless you are considering hunting some of the dangerous game species (ie. buffalo, rhino or elephant) 70lbs is just fine. There are legal limits on draw weight, arrow weight and kinetic energy for many particular animals over in Africa. But a 70lb setup is perfectly fine for most of the animals over there. In fact, you can do quite well with a 60lb setup.
Bottomline, is this guy full of it for saying he shoots that draw weight? Maybe not. But his reasoning for doing so, may be flawed.