I'm very positive that the percentages DLT gave for professional snooker players are accurate, and that indeed you will not find a snooker coach that will teach it any other way. There might be different emphasis on which fingers to use as the main grip (thumb + index, or thumb + middle, etc.), whether to actually pay attention to the unfurling or just let it happen natually, and so on.
I also agree that most fingers need to unfurl when cueing in a straight line (piston style), simply because of the anatomy of the human hand. A video says more than a thousand words:
https://youtu.be/NtpV0qDGRqw?t=217 (best watched in 0.25 x slow motion).
Pay attention to his knuckles in relation to the line of the cue during address (tip at the cue ball). As he pulls back, the knuckles rotate clockwise from the camera's point of view, the little finger knuckle goes upwards. He has to unfurl his back fingers in order to keep the cue in a straight line. When he follows through, his knuckles rotate counter-clockwise, so he lets his index finger unfurl for the same reason. The only way to keep all fingers on the cue exactly the same during the entire stroke, would be to raise the butt of the cue in a pendulum style. And you will not find a snooker player with a pendulum stroke.
Test it for yourself before refuting it: Take your cue, put it firmly against your chest and chin in order to prevent it going upwards, and try a few deliberately slow and long backstrokes. Longer than you would normally for this test. Notice how your elbow has to drop and the majority of your grip fingers have to unfurl. Try gripping mainly with thumb+index, and also thumb+middle finger. You'll notice that all other fingers will unfurl naturally.
One of the longest and smoothest strokes I've seen is Chris Mellings'. He has a snooker background, but got rid of the chin-on-cue and chest-to-cue parts. Watch how his fingers unfurl to the extreme:
https://youtu.be/jh3K-Nz7w-4?t=552