It rather is a strange phenomenon. I read the book Technical Tennis by Rod Cross and Crawford Lindsey - it was a long winter - and they really dig into the nuts and bolts of what physically happens when a racquet and the strings interact with a tennis ball. It includes a whole lot more than what I may have thought before I found this work.
Well, I have this book to hand now and I always had doubts about some of the claims, although it is definitely worth reading if you like tennis technology. For example on page 131 in section "Can racket and strings Increase Spin?" they claim that "lab experiments show that the end result is always the same spin"
I think TW has a video showing poly generating more spin.
Testing dozens rackets every year is sort of my hobby and why some rackets and/or brands always worked better for me than others some things were constant over the years for the frames of the same size:
1) thinner string of the same type generate more spin (like my Technifibre X-one or NRG)
2) gut generate more spin than multi (but not great option outdoors in UK)
3) open string pattern generate more spin.
I even tested poly/multi hybrid (Signum Pro 18/Technifibre X-one 17) first time in my rackets (Head PPYT and Dunlop 200 Bio Lite) for the last few weeks and it definitely generate much more spin than X-one.
Many rackets considered spin monsters like Bab APD or Head Extreme Pro delivered amazing spin for me even if Bab APD "delivered" elbow pain as well.
Rackets measured/published characteristics quite often do not reflect playing experience. I did not have elbow issues with Head EP although it is listed as similar stiffness to Bab APD.
I am surprised by another poster claim that we all can play with 10-13 oz rackets.
Well 10 is very light to me but 13 is very heavy (i.e. great for hitting but not playing). 10 grams in racket weight can make huge difference albeit not as much as swingweight difference of 10.
I could never play with Yonex after trying dozen rackets till I tried 310 Tour version few years back.
I disagree with comments that racket is just 1%. It is not going to allow 4.0 like me to beat 5.0 but racket which matches your game and fitness level is worth few games a set between evenly matched opponents.
If I could play with Babolat APD I would. I won a match 6:1, 6:2 against my regular tennis partner when normally we have very close matches with deuces galore. He commented on power and spin of my strokes.
No idea why it should be the case but it shows that testing is the only way to find your perfect stick, because racket spectrum is so varied.