Here's my take:
Cartridge - 80%
Arm - 10%
Platter - 5%
Plinth - 5%
No love for the bearing? Interesting. The motor I guess is optional equipment too. Probably since the bearing and motor are zero you could just scrape the cartridge by hand. I mean after all that is where almost all the sound comes from. Save a lot of money that way!
Still, fascinating subject. Back in the day we had this thing we all did, it was called changing only one thing at a time. Idea being, if you change a bunch of stuff you just can't know what did what. So we ran around changing only the speakers, and when we heard a system with new speakers and everything else in the system was new too we'd say the system sounded good or maybe that the speakers might be pretty good but they were with all this other stuff we need to hear them again to be sure. By again we meant with all known associated equipment.
Man what a waste of time! We shoulda made one of these lists! Then we could just leave all that other stuff off the list and BAM! Speakers 80%! Yeah, science!
Yeah, sarcasm. Makes the point. What are the odds you're gonna get the percentages right, when you can't even come up with all the things that belong on the list? No bearing, no motor. Also no mass, nor suspension, which if you don't have an awful lot of one you sure need the other. Linn, ring a bell? Also nothing to control the speed of the motor. Power? Zero. Good luck with that!
But even with a full list, how can you even begin to assign percentages? The normal, established, and accepted approach is to carefully change only one thing at a time. That's why we bring stuff home, to see how each individual thing sounds all by itself when added to our system. With turntables then, in order to have any idea at all, you would at a minimum need to change each individual component part, one at a time.
So let's see now.... the first one I did was the belt. Just the belt. Tried a couple different ones. Then the power cord going into the motor. Soldered another one to it. Then the motor itself. Then tried a different motor controller. Then tried the different motor controller with battery power. Hey, I know! Let's make a list!
Bearing: took it apart, changed teflon coated bronze thrust plate for tungsten carbide; changed stainless ball bearing to silicon carbide. Polished bearing shaft to 4 micron finish.
Platter: compared exact same dimensions platters in solid acrylic, lead shot weighted acrylic, a proprietary composite material, and stabilized and weighted Cocobolo.
Plinth: compared several in MDF, and carbon fiber, of different construction and mass, including BDR Shelf.
Shelf/rack: tested a whole range of these, everything from none (sitting right on the floor) to MDF (various shapes and thicknesses), to sand and concrete and granite and carbon fiber and sorbothane and even a few others we will zero off the list because you get the point. I hope.
The rack, or whatever the table sits on, is just as much a part of it as anything else. What is the question again? Oh yeah: Breakdown of turntable performance. If there's one thing I know its that the rack or whatever the darn thing sits on instantly becomes an integral component of turntable performance.
We report. You decide.
What's funny is that in spite of having done all those comparisons and knowing intimately and well exactly the contribution of each part the last thing I would ever do is rank them top to bottom, let alone assign percentages. If forced, if you held my hand to the flame, I'd say they are all equal.
Because if there's one thing I have learned from changing all these things its that every single little thing matters- and none more so than any of the others. But hey, lists are fun. Pretending is fun. Who knows, every once in a while could maybe even lead to learning a little something new.