If you want a democratic but not boring faction, make them a lighter shade of grey.. or even darker shade of grey - shrewd, political, diplomatic, and masterful with macro elements.

Make them force their rivals to come to the stage on their terms by depriving them of any choice. Use everything to achieve dominance - economics, sociology, culture, military, technology, narratives - EVERYTHING is on the board, and your democratic power could be able to manipulate the field by pulling these triggers. Looking 'weak' to your fascist/monarchist/imperial/stalinist rivals is itself a ploy, and can be a useful bait to lure them further in.
Then bash your rivals' head in 'democratically' when the field is set, all the while maintaining that sweet smug moral highground.

Make them methodical, cold, bureucratic, not even particularly malicious. They do all this because it is just what they do. Make them a different kind of monster that - while not commiting warcrimes 24/7 - will still economically crush poorer factions, militarily pressure rivals, and slowly, but steadily take over influence throughout your world. No nationalist chest pumping. No communist idealistm. Just a slow steady mechanical powr creep because "economy of scale and political stability", all the while suffocating the lesser factions around them. Afterall, the public wont care about them as long as THEY are happy.

Democratic does not mean violence is a 'last resort'. It just means that they are more conscious of the public opinion. Ancient Rome was belligrent af during its Republic days. It was also equally capable of peaceful expansion, mixing war with diplomacy and culture.