I've got a steel CX bike from the mid-late 90's (not super sure of the exact age).
It's 700c, basic cross geometry, short chain stay, canti's. 22-23 lbs depending on my mood.
I don't get smoked on it. I usually pass others on it. Mine isn't set up remarkably different than yours and is equally obsolete. I am 100 percent certain that I'd finish most of my rides waaaay slower on yours. I can't imagine riding hard for hours on a converted concerted old skool mtn bike.
It's not the age of the bike in your case, I think it's the design.
It's probably better for lower speed more technical riding and bike packing.