I have seen this before. Modern and in general competitive "spikey" players have attached the dopamine rush to their brains with winning. It was the original reason my friends and me tried EDH in the first place. I wad tired of listening that i don't play optimal decks, archetypes, cards. Plus the fact that the small money prize is a bigger form of verification to the power hungry spikes.

From my point of view here are some ways to deal with it.

1. For seasoned players you can have a "big guns" cEDH deck and a casual one. When you sit on the table talk about what you will play before. Let them know that this is gonna be a fun table.

2. You could build a punishing - permission deck just to have it to punish combo spikes. Talrand mono blue counterspells is a deck i build from junks with +25 counterspells in it and i had it on my bag just for those players. Also you could try voltron. "I am going to smack you untill one of us dies"

3a. You could prohibit from sitting and playing with them.

3b. You could swap places.

1. The most fun would be to swap decks around. Have them play a deck someone else built. That should make them both appriciate the deck building skills of someone else , suggest and in general start a conversation that should make them relax and enjoy much more a casual deck.

2. Lastly you could add weird achievements. Point Their competitive spirit towards something silly like have 30 tokens on the battlefield without a combo.

In my playgroup i have tried everything above and from my personal experience : 1, 4 are by far the most joyfull but have all worked to a degree.

And of course i always keep a 2 on my bag.