There’s roughly ninety veterans in Congress, or about 20%. Veterans compose about 7% of the total US population, so strictly speaking veterans are overrepresented relative to the general population.
However, to your point, just being a member of the military does not necessary make someone trained, disciplined, pragmatic, and understand teamwork and orders. Lindsay Graham, Louis Gohmert, Mitch McConnell, Ronny Jackson, and Tom Cotton are all veterans.
But, so are Tammy Duckworth, Adam Kinzinger, Connor Lamb, Ted Lieu, and Mark Kelly.