You're asking for MOAS too soon. You cannot just pick random numbers.
Election will be won during registration and voting. In last election 6 out of 10 in gema was registered voter. The rest of the country is 3 out of 10. So that made GEMA population exaggerated in relation their population. GEMA as population is merely about 22% now or about. But yes they are in demographic transition so maybe they have more adults. But not that extreme.
Ruto if he focussed on registering Kalenjin - can start with 3-4m votes. Kalenjin are energized more than any group. That should be his focus come January next year when Mass Voter Registration begin.
Outside GEMA - Uhuru was a toxic candidate - he was not sellable at all - maybe Gusii. Ruto is selling in new places like Turkana, MATUSA, Coast and Luhyaland. Even in Luo Nyanza - Ruto can get slightly better than Uhuru

. I believe in contest btw RUTo and Raila - Ruto will score 60 percent outside big 5.
So for Ruto to make up the deficit - 1) Register every kalenjin and make sure they vote - this is GEMA trick the last few elections 2) Win in new areas where Uhuru as Kenyatta/Kikuyu was hard sell.
Finally I don't see GEMA voting elsewhere except for RUto. They have no option. In red corner is Raila who they loath.