Therein lies our difference of opinion. The number of terrorists/insurgents is not constant or finite. It can increase or decrease depending upon the circumstances. Israel has been fighting terrorists for decades and over generations. Insurgencies are not won by body counts, but by convincing the general populace it is in their interest not to support the insurgents.
Terrorist/insurgent wars can also succeed as was the case in Ireland against the British, which resulted in the formation of the Irish Free State. Chairman Mao was also successful.
When I say "finite number," I'm assuming we don't do something stupid and bomb a bunch of civilians who might, otherwise be on our side. Without such an incident, yes, the number is pretty finite.
As for the Brits in Ireland, a better counterfactual would be if a British-supported IRISH government (not northern Ireland) was facing a rebellion, and if it commanded a majority of the Irish population. In that case, England would have won.