I think we all ride for fitness.

Most of us like to ride fast and feel the freedom of a silky smooth ride.

If it we're just fitness, I could drag a cinder block on a rope behind me while riding (which is probably an upgrade to some of the things you see on the road).

Drivetrain friction is essentially a non entity unless something is damaged. The ease of shifting, the ability to stay adjusted, durability, and the steps between gears is what you pay for. And weight, sometimes as a sacrifice to durability.

With your gear ratio, you certainly can climb fast. I don't know your physiology, bike weight, or mentality.

My 1986 Dura Ace group is smooth. It's like the the dark ages compared to my 2002 Campy Chorus group, which again, is barely a drivetrain compared to a modern di2 or comparable.

I don't think you should upgrade your ride. It's sounds great, keep it going as it is. Get yourself a nice 15lb carbon everything ride to supplement it, on the steep days.