I guess that is a matter of the definition of an accompllishment.
Take good old Rooks & Kings for example. They usually did not even have 100 ppl available for their fleets, but whenever one did run into them interesting things happened :).
Sure 100 pilots will not take and hold sov in todays climate, but you don´t need to hold sov to do great thinks an make a name for yourself (as in for your group).
It´s not that it´s impossible to be a real pain in the ass with 100 pilots. The reason why you don´t hear it happening more often is, because eve mostly lost that type of players while ccp tried to make the game more appealing to the mainstream.
You don´t hear anything great about corps with that kind of player numbers, because they all choose to take the easy route of either just renting space or joining the established alliances, rather than doing their own thing.
And the corps which don´t join any of the poweblocks, but have the numbers to actually start some fires don´t do it, because they are run by people who have no interest in burning down stuff and only care about their personal wealth.
While I don´t think 100 ppl can have much of an influence on the political landscape in eve and the distribution of power, it´s still more than enough people to start some fires and to be a pain in the behind for the powerblocks.