Rest less often?
Nothing in the game requires you to take long rests.
I long rest as little as possible even when my main is a mage. (My first long rest is usually at the Druid Grove after I've defeated the Bugbear assassin and the Harpies.
It's your choice.
If you want your Warlock to shine a little brighter only take long rests after every 5 or 6 encounters.
And that is a BS argument, you are essentially saying gimp your other characters to make your warlock seem balanced. That isn't a meaningful choice in terms of gameplay, that is a meta choice on whether or not you want to play with a self imposed handicap. Yeah, you can polish a turd, but it's still a turd no matter how shiny you make it or how much you wish it were something else.
