It seems you were invaluable to this startup, and the founders seems to be aware of it. You are in a good position to talk directly to them about the issue. Be

It seems you were invaluable to this startup, and the founders seems to be aware of it. You are in a good position to talk directly to them about the issue. Be professional, and if the founders are thinking rationally they’ll hopefully act to create the good environment for you because they like you and your work, and maybe remove the team lead. If they are not, then they are not considering your contribution to it’s just value, and/or they are not courageous enough to act. In these case you can leave with peace of mind, to find a place where you and you work will be more appreciated. (Sorry for my limited English)