just think of what would happen if you make alliances smaller
groups that are now large would break up and bunch togethet into coalitions of alliances
in fact with just 50 people it is so hard to protect center and beat the opposition already that it is common to form coalitions and be forced to split medals
this means that the optimal size of alliances for controlling a world is larger than 50, not smaller
the rest is human nature
the grouping of players is primary, the size restriction on alliances is secondary, on competitive world's at least
i.e. there is no way to make it easier for a small alliance to win, except by removing competition somehow
regarding fun, there are ways to make the game more fun, but playing with the size of alliances is not one of them