He is absolutely right: Don't cut springs because it ruins them by changing the spring rate. If the spring rate is way off, the shocks fight
the springs in controlling the rear axle. This makes the car's rear end dance around. A dancing rear end is WOW! on a hot girl but not on
a hot car.
Lowering a car after using a 2" lowering spring leaves you with almost no travel for the real axle to go upwards before it hits the bump
stop. Bang against the bump stop often enough and you
will break something...
Jack up the car, put jackstands under the both sides of the rear axle so that both wheels are an equal height off the ground.
Then remove the rear wheel on either side. Measure the distance between the bump stop and the place on the axle where it hits.
The amount of travel you have left is minimal at best.
And he is being nice to you... I'm surprised he didn't blister the paint off you car...