You came up with a great idea. In Heroes, in the campaigns, on normal difficulty levels, they should introduce a "troop limit." In theory, this would solve the problem of "numerical superiority."
P.S. Although I'm more than sure that this system would have many drawbacks XD
Then it would be better to introduce a time limit; this would also help, and this system wouldn't have any drawbacks.
Демократия есть одурачивание народа при помощи народа ради блага народа.(Уайльд Оскар)