Jim Clark- you could say he would have won more, maybe the team just worked for him. However his results post 2nd win? Senna? Who knows? Death robbed him of that title with Williams. Was he pushing too hard?
Being a gifted drivers, one of the greats however the best for me win in more that one Marque, luck/getting into and developing the best car for that season- doing that in a new alien team again? = the greatest for me.
I grundgingly put Schumacher up there with Prost (see his list of 2nds etc?). If Lewis goes into another team and wins titles with three constructors I’d call him the greatest of them all.