I have used death metals in a boss fight. It's pretty much the only thing i save them for. I'm not saying there aren't benefits that can come from reviving in the middle of a battle, im saying that it's not impossible to think that you can work yourself into a corner where you're screwed on gear and resources that constantly reviving would just be a waste. This fundamentally goes against what p2w is, at least in the context of boss battles.No you are temporarily invisible to the boss after using a coin. You must have never used one before. You can wail on a boss with no consequence and do huge damage. It does become 100x easier.
Now, if it were a situation where each revive gave you back all your gear and resources from before the fight then that be a different story.
I think a lot of the complaints about P2W would tone down if there were a way to avoid the TDM. As it stands, you're always on edge about how many coins you've got on you. It definitely creates a strange landscape for progression. I'd love to be able to spend a DM for a few days of protection. That would be worth it to me.
This sounds way more p2w than anything that's in the game now