Its not any longer a question of overkill but of economics. In every sense you are asking the wrong question and we are having the wrong debate.
It costs less to fit a G1000 in a new aircraft, so that is what they come with, and its what they are designed to accept.
I dont think anyone would contemplate fitting a G1000 in an existing aircraft and I dont think anyone would buy a new SR22 and ask Cirrus to fit a six pack.
If the salesman had to pitch glass or an optional six pack "upgrade" at +$10,000 I dont think he would get many takers.
In reality the only sensible question is should manufacturers be fitting glass or dials given glass is cheaper. The only reason I can think of is serviceability, in every other aspect glass wins hands down.
Perhaps if you wanted to operate a Cirrus in Outer Mongolia it would make sense to custom design a six pack installation, but then maybe a Cirrus would not be the best aircraft in the first place!