This is just laughable. There's no actual argument here. The idea that having vastly less HP is fine because "above level 16" (a range no-one plays in) WIS saves are common is hilariously nonsensical. Even enough CON to get +1 HP is a gigantic boost to real-terms survivability - If you have a d6 HD, that's about 30% more HP per level (ignoring the L1 max HP, but we can factor that in if you want to be difficult - you'll be doing the maths though). d8, it's still about 25% more. d10, 20% more, and so on (also it's slightly less of gain with fixed HP/level, but only slightly - what like 5% less?). +2 or more is amazing.
To be clear Wisdom is more important at low level, above level 16 (where I have played 6 different characters in campaigns and more in one shots) Wisdom proficiency is pretty important.
I am currently playing 4 regular games per week, I have played numerous characters with a 10 Constitution and 10 or 12 is the "normal" Constituition I play with in a point buy game. On point buy I have never played with higher than a 14 unless I got a boon to boost it from the DM and I normally only play a Rune Knight or Damphir at 14 and that is because their subclass abilities and natural attack respectively key off Con.
I've played enough 5E to know HP are absolutely vital when stuff gets real. +WIS isn't terrible - it'll be far ahead of INT, CHA and STR if those aren't primaries for you (for combat survival specifically), though probably not DEX due to Initiative. But the idea that WIS saves are something that happen constantly and always has terrible consequences is failed is utter bollocks - most sessions pass with zero player-side WIS saves - and even those that happen are rarely Hold Person or the like, but like with CON, usually for lesser effects. CON is used for plenty of equally-fatal effects too - like Paralysis and Petrification.
Wisdom is far more debnilitating generally, Constitution is used for some paralyzation (less often than Wisdom) and rarely on a stright up save. Normally you need to get hit first and then you make your Constitution save as opposed to Wisdom which is usually just a save right out of the gate. All the petrification conditions I know of in game require multiple failed saves, the first of which causes restrained (like I said).
And HP is the only defence that really works at that point.
No it doesn't. At 5th level a +2 COnstitution is 10hps. That is not even a single hit while you are paralyzed.
So over say, 100 incidences of Hold Person being cast on a PC, I daresay the CON PC will survive more than the WIS PC.
You can say this, but you would be wrong, remeber you save every single turn.
We can put this into whiteroom against a weak opponent:
a 6th level fighter with a +7 attack, 17 AC and a Longbow with a 0 wisdom save fighting a Wizard with an AC of 21, dex of 16 who casts hold person with a DC of 15 and uses booming blade with a dagger when the fighter is held and recasts after a save at the end of the fighters turn.
In that whiteroom with the Wizard winning initiative the fighter with a 0 wisdom save, +2 Con and 52 hit points will last on average 12.5 rounds against that Wizard and will deal 10 damage total to the Wizard over that 12 rounds.
In that same Whiteroom with a +2 Wisdom save and 40 hit points the Fighter will survive 13 rounds and deal 18 damage on average over those 13 rounds.
That is against a single enemy with a weak melee attack. Give the Wizard some allies and it tilts even further away from the fighter.
We must admit it is impossible to calculate because it's fully situational (Hold Person is meaningless if no enemies are in position, physically and Initiative-wise, to take advantage, and probably instantly fatal regardless of HP if several are).
Stopping actions is pretty meaningful. Every round the PC is held that is damage she is not doing or enemies she is not controlling. But that is the reason I used an example with a weak melee attack in the example above.
I agree if there are a lot of enemies to take advantage it is instantly fatal regardless of hit points, and this underscores my point - the extra hit points you get from Constitution are not very meaningful.
The idea that tanks don't need CON unless they're Barbarians is just not even arguable though. That's such a bad claim that you should retract it.
They don't. If they are optimized it is better to have more hit points than less, but they are not necessary. A high AC beats a high Constitution every time and more hit points can both be replenished and added relatively easy through magic.
I have played a ton of 5E and most of it in the last 5 years has been played with characters with a 10 or 12 Constitution, many of them tank builds and they did fine. Have you actually tried playing multiple 10-12 CON characters in a level 1-20 game like I have? If you have not tried it maybe you are the one who should retract your statement.
This is going to be even more true in the new rules where using potions will be a bonus action. Part of this now is that being at 0 hit points is actually better than being paralyzed or incapacitated from a spell or effect, because it is a lot easier for your allies to fix.
Here are two examples of a character with a 10 and 12 Constitution who I played to level 20. These are not the best examples, but these are the best I have character sheets for online. Both of these PCs could tank well.
The World's most intelligent Dungeons and Dragons Character Sheet.
www.dndbeyond.com
The World's most intelligent Dungeons and Dragons Character Sheet.
www.dndbeyond.com