In earlier editions there was a common issue of characters having a "Christmas Tree" of glowing magic items. The limit of three was directly put in to address this point, which powerful items need attunement so a character will only have a few of them.
This addressed a pervasive problem in earlier editions. I wouldn't want to change that until I had an alternate way to limit items a character had.
Now, where I would change attunement is make it more like Earthdawn, where you need to learn more about the item to unlock it's abilities, and you can unlock more over time and have the item grow with you.
What I do is that if a character drops to 0 hp they get one level of exhaustion. That level can be removed during a short rest. However, for each failed death save they gain another level of exhaustion that can only be removed in the normal manner (i.e., one per long rest).
It tends to get rid of the jack in the box heal/die cycle.
Hmmm...I thought that with an unconscious person a 'coup de grace' was automatic if they so chose. I'm used to just whacking people into fillets or hamburger, but still...
"Damage at 0 Hit Points. If you take any damage while you have 0 hit points, you suffer a death saving throw failure. If the damage is from a critical hit, you suffer two failures instead. If the damage equals or exceeds your hit point maximum, you suffer instant death."
As you can see, it's only one death save unless you get lucky and crit. The instant death I just don't see happening once you reach mid level or higher. The system gives too many hit points to do that in one strike.
But a melee attack against an unconscious foe is automatically a critical hit, so your first hit should have given him 2 failed saves and the fireball would have killed him.
I prefer trait based numbers as well - but even if you wanted to keep 3, you could do this as items above 3 start causing magic toxicityMake it more like Cyberpunk. Use an existing Stat or create a new one...or make it a number based on a combination of stats and that number lowers the more numerous/powerful items you have and have those items slowly drive you crazy. There was a reason Gollum succumbed to the One Ring....MOIHAHAHAHAAAA!
For me, I'd say it's a confluence of poor indices, the amount of cross-reference required