As of 4:00 PM on Dec 25, 2022, based on OP.GG Platinum+ data *Ivern, Skarner, and Aurelion Sol are RIP so I assigned them: Jungle, Jungle, and Mid respectively *Since this is based on OP.GG stats, stuff like Top Lucian (which doesn't show up anymore) isn't here, but picks like Miss Fortune support—which are completely troll—are still included since they do show up
1. Single role champs: 101 total
Top: 21 (Fiora, Darius, Aatrox, Olaf, K'Sante, Nasus, Kled, Illaoi, Quinn, Shen, Kayle, Urgot, Riven, Ornn, Gwen, Volibear, Kennen, Teemo, Yorick, Nasus, Sion)
Jungle: 21 (Elise, Kindred, Rammus, Evelynn, Master Yi, Vi, Udyr, Nidalee, Bel'Veth, Kha'Zix, Rek'Sai, Nocturne, Kayn, Karthus, Hecarim, Shyvana, Xin Zhao, Jarvan IV, Trundle, Ivern, Skarner)
Mid: 18 (Vex, Katarina, Kassadin, Viktor, Galio, Fizz, Ahri, Qiyana, Cassiopeia, Zoe, Malzahar, Veigar, Twisted Fate, Orianna, Lissandra, Annie, Corki, Aurelion Sol)
ADC: 17 (Samira, Kai'Sa, Jhin, Caitlyn, Lucian, Varus, Nilah, Tristana, Ezreal, Zeri, Jinx, Draven, Sivir, Xayah, Kalista, Kog'Maw, Aphelios)
Support: 24 (Blitzcrank, Nami, Pyke, Nautilus, Rell, Thresh, Rakan, Zyra, Sona, Lulu, Zilean, Soraka, Morgana, Leona, Yuumi, Renata Glasc, Janna, Bard, Vel'Koz, Alistar, Taric, Senna, Seraphine, Braum)
2. Multi-role champs: 61 total
2-1. Dual role champs: 54 total
Top/Jungle: 11 (Warwick, Dr. Mundo, Camille, Jax, Poppy, Mordekaiser, Rengar, Wukong, Sejuani, Lillia, Graves)
Top/Mid: 15 (Gangplank, Irelia, Malphite, Garen, Renekton, Tryndamere, Jayce, Akshan, Singed, Vladimir, Yone, Cho'Gath, Yasuo, Ryze, Akali)
Top/ADC: 1 (Vayne)
Top/Support: 2 (Kennen, Tahm Kench)
Jungle/Mid: 9 (Sylas, Ekko, Nunu & Willump, Diana, Lee Sin, Viego, Taliyah, Zed, Talon)
Jungle/ADC: 0
Jungle/Support: 3 (Fiddlesticks, Shaco, Amumu)
Mid/ADC: 1 (Ziggs)
Mid/Support: 9 (Karma, Anivia, Neeko, Syndra, Lux, LeBlanc, Brand, Xerath, Azir)
ADC/Support: 3 (Ashe, Twitch, Miss Fortune)
2-2. Triple role champs: 5 total
Top/Jungle/Mid: 1 (Rumble)
Top/Jungle/Support: 1 (Maokai)
Top/Mid/Support: 3 (Sett, Swain, Pantheon)
2-3. Quad role champs: 2 total
Top/Jungle/Mid/Support: 2 (Zac, Gragas)
3. Notable observations
The ratio of single-role champs (e.g., champs that only go Top) to the total champs in each role: Top 36.8%, Jungle 45.7%, Mid 31.6%, ADC 77.3%, Support 51.1%. So ADC > Support > Jungle > Top > Mid.
If you just count raw numbers of single-role champs, it's Support > Top = Jungle > Mid > ADC. But the ratio shifts as mentioned because the total champ pool per role is 57, 46, 57, 22, and 47 respectively—ADC just has very few champs in total.
Every champ that can flex into three or more roles includes Top, and none of them include ADC.
Even among dual-role champs, the ones that mix in ADC or Support are rarer than champs that flex between two top-side lanes. The only exception is Mid/Support, which has a fair number thanks to mage supports.
Probably because it's preseason, I see a lot of people picking champs that belong to other lanes (especially Mid) in the support role just for fun—like Anivia, Syndra, LeBlanc, Azir, Twitch. I was on the fence about excluding some of them, so I just lumped them into dual-role. But considering they're basically dodge-bait picks, the actual percentage of pure Mid champs and pure Support champs is probably higher than what I calculated.