Back in the day's the spirit weapons were the equivalent of S and R grade weapons in comparison.. It had it's own artwork and animation with the attacks and was an ally in combat as you can use their awakening attack a handful of times before charging again. Remember this was when windmill was the most powerful mobbing skill at the time....spirit weapon awakening was the next skill that could help demolish a roomful of formor hoards.
It is going through a revamp as we speak. KR already stating they are trying to figure out how to rework the spirit weapons.
Ur missing one other reason. Unique dye schemes. Some weapons uniqueness can only be obtain via this method and abusing the transfer method. ^_^
It's a way to individualize the player character in game. As any given character can only have 1 spirit it becomes a choice to what you want to work with.
Nothing because Gacha is not the same as loot boxes and the only people to blame is yourself if you buy gacha and you dont get something, that's not nexon's fault because you are not being promised something good. ALso doing Gacha is not gambling, if you are at the point were you can't control yourself, that's not nexon's fault.
I mean you can say all trading cards/blind bags are gambling and no one is whining over them.