Eh I think some of these are a little iffy to include on a list like this.
Garuda (FFIX) - I mean ANY enemy you encounter in an area you're not really supposed to go that early could cause a frustrating reset, but it isn't really the enemy's fault in that case is it? It's your fault for being where you shouldn't be.
And if you're going there specifically to get Quina White Wind early, then it kind of ceases to be RANDOM since you were deliberately looking for this enemy. In such a case you would obviously save before hand and, as you admit the ability is available later, I don't see why this should be included in a list of particularly dangerous RANDOM encounters.
Red Giant (FFXV) - The game literally tells you from the start that Daemons roam around at night and warns to avoid travelling in the dark. You should know full well what you're getting into if you decide to not camp when its getting dark. Point being that it's not really RANDOM if you KNOW you'll fight Daemons in the night time.
Sure the Red Giant could be particularly strong but by the time you have no choice about travelling at night I'm sure your better equipped to deal with shit like it.
Great Malboro (FFX) - To an extent, I kind of agree with this one. At least in the context of encountering Great Malboro before getting Auron's celestial weapon (which kind of renders him completely moot). My issue is that he maintains that it's still a threat even after that.
I mean no, if you get fucked by Great Malboro's Bad Breath when you already have Masamune, you kind of deserved it. It's not hard to just keep Auron in the battle team and one-shot it. Sure capturing them can be a bitch, but you're looking for them in that scenario and they cease to be random.
Don't have a problem with the others, just the logic behind including those three on a list of hardest random battles is a bit iffy.
