JUST LET YOUR PLAYERS BE AWESOME SOMETIMES

I know it's frustrating if your player is a golden god at dealing with some types of situations which defeat your effort to make a challenge for them, but this is one of the cheapest and easiest ways you can enable them to have fun in your game. There will be other situations which present genuine challenge, but it doesn't all have to be super hard. It is okay to let them flex.

What's the point of the mechanics including badass abilities if you're gonna get all frustrated if your players start to become badass sometimes

I agree! There are limits to it all, but its up to you as a dm to make it fun for everyone and letting players flex is included in it! I have a lvl 5 paladin the dm has huge issues hitting and its hilarious sometimes! That said, i cant for shit so this makes it fun for the dm as well. My team mates have once just looked at me and the last skeleton warrior duke it out while the rest was dead. It couldnt hit me and i was constantly missing my attacks. We were all laughing our arses off haha