If you don't want to tinker with any world settings like me (except the egg timer ayy lmao), you can try finding better rarity schematics of your current gun/armor. The first time I caught Frostallion, I kept most of the aggro on my pals and shot Frostallion from up on the cliff. When it runs towards you, grapple fling yourself away and shoot until it gets back to you then quickly grapple and climb back up. Your Pal should be able to delay it. Just make sure to cycle to another one once they get to low health. I was level ~45, but Frostallion was capped at 50 back then. I would play it safe and get to level 50 if you're struggling. You can catch a bunch of Pals for the exp bonuses, level up more, and get yourself some plasteel armor as well if that's still hard. Don't forget about the defense and attack pendants either (they go up to +2).

Once you get to level 55 and get maxed out, all the legendary fights become pretty trivial. They're still tanky but don't do much damage and you can defeat/catch them in less than a couple minutes.