My first road bike was Columubus SLX steel, nice, but stiff and punishing.
I rode an alloy bike 45 miles and felt beaten up.
I wondered how I was ever going to build up my miles if road bikes were so punishing.
Then I got a carbon bike and it was a revelation. Now I ride 50-60 miles at weekends and don't feel beaten up, just tired legs.
You probably had too much pressure in your tyres!
It's such a shame that blind tests can't be carried out on bicycles, As regards 'stiffness, compliance and material' bollards, most normal cyclists wouldn't be able to tell the difference if they didn't know. It's all subjective.
To OP, ain't you got a bike yet!