I wrote this for the ASOIAF subreddit and I thought I'd share it here too.
Correct me if I'm wrong, but has there been a battle in HBO's Game of Thrones since Season 4's battle at Castle Black which did not feature a near-complete wipeout of one side? Historically it was a disaster to be decimated, and decimated only means losing 1/10th of your forces. It's rare for armies to neither surrender nor retreat when a battle is clearly going against them. It certainly shouldn't be happening in every battle.
In most of these cases, it seems the purpose is to remove the army as an element so we can focus on 1 v 1 character fights, no matter how ridiculous or contrived or disastrous.
Stannis vs Boltons
After many desertions, Stannis has a complete wipeout against the Boltons. Refusing to surrender to a man is not a normal thing, but it's Stannis vs. Ramsay, fine whatever.
Hardhome
A handful of boats aside, near complete wipeout of the wildlings present. Fine, it shows the threat of the WW for what it's supposed to be and puts Jon in the position of fleeing the massacre.
Battle of the Bastards
Virtual wipeout of Snow's forces after some contrived stupidity. Snow acts like a moron with no restraint and ends up surrounded literally in a pile of bodies of his allies. All so that it can be completely desperate when Sansa, Baelish and the Vale knights can come in to save the day. Complete wipeout for Bolton forces and similarly pushes towards a 1 v 1 confrontation between Jon and Ramsay.
Battle of Winterfell
100% wipeout for WW (possibly the entire race). Visually we see a virtual wipeout of the Dothraki. In the after the episode they even say that it is the end of the Dothraki race. We later see what appears to be a wipeout of the unsullied and all the other infantry as well. By the end of the episode it looks like a complete wipeout of everyone bar named characters. With all the grunts dead, we get to have named characters swarmed by wights or 1 v 1 the Night King (each individually). I guess this one's ok, because despite what they show on screen and say in after episode - it turns out only 50% of winterfell forces are destroyed. 50% is a good result by the standards of recent GoT battles In later episodes it looks like the Unsullied are even stronger than before the battle.
Battle of King's Landing
Complete wipeout of Euron's fleet. Complete wipeout of Golden Company. Lannister armies look to be surrendering in the city, but then we get a complete wipeout of not just the army, but the civilian population as well...
I didn't watch Season 7 so I missed the battles in that one. Just based on the ones I have seen I imagine those featured total wipeouts as well.