There is many parts you can do better on a bike. Improve aerodynamics like a Venge Vias. Improve the weight like my SuperSIX Evo I had:
You can improve the fit of your bike with a BGfit for example:
But a thing you can’t improve on a bike is the geometry. The last thing you can change and then you change bike.
Like the Trek Madone 6.2 I had last year:
It was superstiff and it felt really fast, really fast. The biggest downside with that bike was that I didn’t use it enough😉 but also the toptube, it shouldn’t make any difference but I felt it was too low.
And yesterday after riding my Specialized Crux cyclocross on road and a bit fast it didn’t feel as good as a roadbike. Because of geometry.
My Crux feels faster than my old Cannondale SuperX but they are pretty similar in geometry except bb height, chainstay length and the fork. Small small changes that makes a difference.
Cannondale have their Synapse, Specialized got their Roubaix as the best example. They are a bit longer, not as racy as a SuperSIX Evo or a Tarmac. People may talk about weight but it doesn’t differ so much if anything. The big thing is geometry and the small changes that makes the complete feel of the bike differ.
I believe that brands that have been on the market for a while with great success makes bikes that handles better than brands that just put their sticker on a cheap frame from China. There isn’t from nothing people talk about the riding feel of riding a nice Colnago for example.
Have you ever thought about geometrical differences between frames before changing roadbike?