How to handle strong pcs?

Greetings, I will say this now just to make things clear. I am not mad at my players because they rolled their stats well, work well together as a team or even because they had creative ideas during combat. I support all three of those facts and am actually kind of happy that it is the case.

What I wanted to ask is how some of you guys when you were DMing handled situations were your players absolutely demolished your creatures in an encounter. And I do mean demolished. I have made some Kobold Variant Statblocks, stuff like a Warrior, a Archer, Scout, Shaman etc.

This was because we're are currently playing Tyranny of Dragons and I had planned a surprise encounter for them should certain things like up, like a certain amount of Kobolds and Cultists escaping encounters. Things lined up and there was a pretty strong wave at the Greenest Fort. I had imagined it as a mini version of the Helmsdeep from LOTR, at least atmospheric wise. Two of the players came up with a improvised molotov cocktail and were basically able to kill of 70% of the wave. Yes I know Kobolds are not tanks. And I did reward them with some bonus XP because none of the Guards at the Fort actually died because of that.

But it still sacked because that was meant to be the encounter to introduce them to these variant kobolds. I have implemented them in future encounters, but I wanted to know if some of your had similar experiences and how you handled them.

I am sorry if this post is a bit here and there, I have trouble focusing at the moment due to how late it is. I thank everyone for reading in advance.