It used to be like this, and it was horrible. FFXIV has way too many high lv aggressive monsters laying around in every map, you could be happily gathering or doing quests to get one-shotted by a a lv 80 aggressive monsters, that you didn't even know it existed.

At least know you see their red icon and know they will aggro, and you can do your best to avoid them, or just run for the hills and try to survive