Pajeon is a fried batter with things in it, and the batter is thick. A restaurant pancake uses about 120g of flour and starch plus an egg, which is 335 calories before it touches the pan. Then it fries in 20g or more of oil on a hot griddle, and the crispy edges everyone fights over are where that 180 calories of oil sits.
The seafood and scallions are the healthy part and the smallest part. 80g of squid, shrimp and clams is about 80 calories with 15g of protein, and 60g of scallions is 20. If you made the same pancake with double the scallions and half the flour, it would be about 400 and taste better, but no restaurant does that.
At 15,000 to 20,000 won a plate it is meant for sharing, and two people usually split one alongside a kettle of makgeolli. Half a pajeon is 300 calories, and a 750ml bottle of makgeolli is about 340 more, so a rainy evening at the jeon house is 640 per person before the second bottle.