True, but only if Ground maintains market share and some level of acceptable service. I also hear many complaints about Ground, but the shippers choose price over quality most of the time.
If Ground goes down, it takes the rest of the company along for the ride.
Complaints aside, I see nothing to suggest Ground is going down.
You would be surprised at how many people remark about the price/service difference favorable to Ground. If a package three states away comes Ground for $38 and arrives in two days compared to overnight for $146 or 2DA Express for $112 it's usually a simple decision.
Now back to the complaints...
They are statistically small. I know they bolster your argument, and the raw number may seem significant. When taken with respect to the millions of deliveries and pickups made by Ground, that number loses a lot of it's relevance.