The point remains that "optimal" and decisions about what is optimal varies greatly by campaign and by party. A group with strong healing might not make 4hp for the wiz more important than keeping that fog cloud, hold person or hypnotic pattern or levitate going.
In quite a few cases, controlling one key guy while the minions be minions can turn a tough encounter into an easy one and being able to manage thru several low damage minion hits and keep concentration is big. Quite possibly they font get near beating the healing rate fast enough to get the wiz at a point where that 4hp would be key.
But if getting attacked to you drives you to see getting an extra hp per level as better than advsntage on concentration for key spells, my guess is your combats look or play quite different.
As always, it comes down to the challenges but I have to say I have never seen a wizard use their 4th level option for +2 Con but have seen it used for WarCaster more than a few.
Now, I myself am fond of other feats at 4th - like Mage Slayer as I tend to ho more active than resistant early- but that varies a lot because each character, party and campaign are different. But WC is up there on the priority list and taken at 4th it's really for 5th threy 7th and there are some key concentrations there too.
Hmmm. Very odd.
I see what you are saying, but I have never seen it at the table. Two players of Druids (one moon, one land) have taken WC to help ensure that their summoned pets would stick around.
We have had 4 wizards over the 5E years (IIRC) and none of them have taken it, even at higher levels.
By the way, I too have never seen a wizard take +2 Con. It just seems as good of an option for a wizard at level 4 if the DM often targets him as war caster. It helps on saves and it helps with hit points.
Even with WC, his concentration spell stays up, but he still typically has a foe in his face or shooting stuff at him.
Let's look at the math. A wizard with CON 14 (which happens almost all of the time at level 1 at our table) saves on any attack of 21 or fewer damage 65% of the time.
If he takes +2 Int, 5% of his cantrips and spells work when they wouldn't have worked. 5 encounters per day, 4 round encounters, he gets in one extra success.
To match this success with the advantage concentration save, his 65% goes to 87.75% (a 12 CON goes from 60% to 84%). So, about 1 time in 4.5 that he is concentrating would he makes a save that he normally wouldn't make. But if he is concentrating, chances are that he is not standing out in the open so that foes can attack him (at least not at my table). And if he isn't concentrating (which is what actually happens at low level due to the limited number of spell slot and prepped spells), than WC isn't helping him. So in the 5 encounter day, on one encounter IF he is (typically) out in the open and being attacked, it would help. If he is not out in the open, it doesn't help. If he isn't attacked (my preference as a wizard), it doesn't help. If he is attacked in a surprise round, it typically doesn't help (cause he doesn't usually have a concentration spell up before combat unless it is Invisibility or some such).
Heck. Out in the middle of a field, a wizard could cast a spell, fall prone and be safer from ranged attacks, stand up on his next turn, cast a spell, fall prone, rinse and repeat and probably not take much damage until foes got within melee range.
All in all, the +2 Int will be more helpful more often.
But like I said, create a poll. Ask the community how often wizard PCs take WC at level 4. Argumentum ad populum doesn't prove how often WC would help, but it would illustrate how many people tend to agree with you.