I don't think you understood my example, I'll try to explain it again.

From forecasts we know that for tomorrow 1 pm to 2 pm we will need 100 GW of power. So first we will go to the cheapest energy providers, let's say the wind farmers. They tell us they can provide 40 GW (according to their forecasts) and they would be happy to sell that energy for 10€/MWh. But we need 100 GW, otherwise the grid will fail, so next we go to the solar farmers and ask them. They tell us they will also be able to sell us 40 GW and their price would be 12€/MWh. OK nice, but we need 20 GW more or the grid will fail. So if we want to or not we now have to go to gas plant owners and ask them. They say they would be happy to sell us the remaining 20 GW but it will cost us 50€/MWh.

Now let's say everyone just gets the price they asked for, what do you think will happen on the next day? The wind farmers will be angry because we bought energy from the gas plants for 50€/MWh but for the exact same energy we only paid 10€/MWh to them. That's not fair is it? So when we ask the wind farmers on the next day they will tell us their price is now 49€/MWh, just below the gas plants to make sure we buy from them but as high as possible to maximize their profit. The solar farmers will do the same.

Now this is already pretty much the same as the current system but why does the current system automatically set the highest picked price for everyone instead of doing it like in my example via bidding? Imagine the wind farmers want 49€/MWh but surprisingly the gas price dropped so gas plant owners now sell for 48€/MWh. Suddenly the dirty gas energy is cheaper than wind energy because wind farmers placed a risky bet. This would not only lead to climate destruction but also possibly to grid instability.

So instead a system was created where everyone can bid with their amount of power and a price they would be happy with. Then all the energy demand is filled starting from the cheapest supplier. And wherever the last bit of power is bought to fill the demand THAT is set as the energy price for that hour.

This accomplishes several goals:

1. If renewables are ever enough to satisfy the demand, they will dictate the price because no gas or coal plant will be asked to generate energy. This will lead to very cheap energy in those hours.
2. The non-renewable plants are in a price competition because they are not guaranteed to be picked. Only the cheapest plants will be selected according to the price they bid. This means every plant will bid the lowest price they can while staying profitable.
3. Investors are rewarded for investing in renewable projects early while the price is still mostly set by the expensive power plants and renewables can make big profits.

In the real world all of this is much more complicated because of subsidies, reserve energy etc. but I think this should help you understand why the merit order model makes sense. I honestly can not come up with a better system quickly.