Every class gets to BE their class all the time every day in some shape or form. They have the CHOICE to be that.
The Barbarian gets Unarmored Defense forever, and at level 2 they could Reckless Attack ALL the time if they so choose.
Casters get cantrips they can do forever.
Rogues can sneak attack all day and can use cunning action and expertise all the time.
Fighters get their Fighting Style
Monks can do that bonus attack punch all the time and get their bonus damage to unarmed attack and their unarmored defense...
Granted, the Rangers and Paladins are a bit outliers in that sense. A Paladin doesn't have any 'always on' abilities until they get a Fighting style at level 2 (at which point, now, they could get cantrips!). Rangers have 'always on' abilities but they're rather lacklustre... but they get their favored terrain all the time and a Fighting style at level 2.
The Battlemaster doesn't get to be a Warlord all the time. They get two rounds a fight, usually. They can't CHOOSE to spam their warlordy-ness, they have to conserve it in case some important fight happens later! And anybody who has ever hoarded potions in a video games will tell you... sometimes you hold on to those things for far too long.
You don't need to DO Warlordy stuff all the time to be a Warlord, you just need to be ABLE to if you so choose.