Sim
Nah. Boss two/three shotting high vigor characters scream lack of balance and cheap difficulty.
Bosses shouldn’t have endless combo streams that can one shot a 50 vig character.
Vigor isn't the only thing you have to rely on in order to tank more hits.
You can also increase your endurance so you can carry the heaviest armor without "heavy load" status. These can add some extra damage absorption.
There are also talismans that reduce physical/magic damage and they stack with other damage reducing potions/flask mix.
If you can't avoid hits by rolling, invest on a great-shield and increase your guard stat. You can further improve your guard using a talisman and even tank hits without losing a single stamina point if you can spam a certain guard boost ash every few seconds. I have a tank character like this and even though there are still a couple of bosses i can't beat yet, nothing can 1 or 2 shot me. I can even absorb a full combo or a surprise grab attack. Not sure if you can achieve something like this with a spell user who can't carry a heavy shield and armor but i do hear how these characters are even more OP so i don't doubt they also have their own damage absorb ways.
Elden Ring also allows you to use a Spirit Ash NPC in most (not all) boss fights. Even though most of them will die very fast in a 1 vs 1 against a major boss, they are still good enough to distract him for you to pass a few free hits or to safely heal yourself mid-fight.
Another thing that helps are the Great Runes. Those are activated using "Rune Arcs" and are finite like the humanities in Dark Souls and you lose the one you have after you die but you still have many of them (i have like 30 mid-game) and i think are farmable. They can be a major buff against boss fights. I mean, one of them increase your stats for as much as 20+ levels or something. So you get extra HP, damage absorption and attack power on top of everything i mentioned above.
All these things stack. And i'm sure developers made the bosses hard enough so you can fight them fully buffed like this. If you go there with just "50 vigor" expecting you will survive, you are going to have a bad time. You need to stack/buff as much as you can.
The only thing that sucks about some bosses is how much of a damage sponge they are. Even with a fully upgraded 2H weapon attack. you can still chip away only a tiny amount of HP. So with some of them it becomes an endurance fight that can last too long.