Under your view of how the game should be, then only extremely large alliances would stand any chance at owning territory. Out of those hundreds of people, only the 5 most dedicated h4dc0r3 gamers would be able to experience GvG combat. What else is everyone else going to do? Do quests to save up 190 skeleton boners to buy a new reputation cloak?
Instead of having a few behemoth alliances duke it out for world domination, a system where smaller guilds and alliance can thrive will generate more organic conflicts and battles between neighbors. There will be more 5v5 teams contributing to more overall fights.
Again, how does this help smaller guilds? The same outcome will result (I doubt a smaller guild could match the gear tier of a larger one) it will just take 3 days rather than 2.
The advantage that bigger guilds have over smaller ones is not the result of attack notification notices. Its a fundamental part of the game, they progress faster, have more silver, more food, and more people.
It doesn't solve the problem.
Shortening attack timers makes it much worse though.