As long as i get to be the frog
I think you have to focus on abilities that evoke the theme.I should also clear up that its not that I don't think there isn't design space for a Warlord. I just don't think there's design space for 4e's Warlord.
The Warlord could make use of mechanics that rarely get used in play, but I'm still looking for that oomph. Hmmm...if I were to go about it, I would have Warlords have 3 main mechanics: allowing immediate rests, letting a player's action ability (casting/attacking/etc) cost only a bonus action, and making a monster temporarily lose resistance/immunity or gain vulnerability from a damage type (including nonmagical damage types).
So maybe the key level 1 feature would be some forms of shouts that the warlord can choose that makes a single creature do their action as a bonus action and the number of creatures they can shout at increases as they level.
Level 2 feature allows them let allies immediately rest and that scales on Charisma.
Level 3 feature is a DC 8+prof+cha save spell that causes the enemy to have vulnerability to certain elemental damage or lose resistance/immunity to BPS damage.
I'm just throwing stuff out there, though.
One might focus on the planning and execution qualities of leadership since there’s already a lot of inspiration themed stuff in 5e.