Nothing wrong with a Con of 14. That's a +2 hp/die and a +2 to Con saves. Pretty robust in any scale that isn't skewed by the stats of player characters.
It's bad when it only gives you a +2 save against a fairly mean spell though! I was expecting a higher Con and/or save proficiency to make a creature like that fairly immune to a certain type of spell and I was dead wrong.
It really took until I started DMing 5e to realize how many creatures actually have terrible saves to protect them from some really debilitating effects. If you're rocking a DC 15-16 save DC, only having a +2 save is pretty rough.
It's bad enough for players, but at least they can take steps to mitigate it. Like, we were up against an enemy that had a blinding aura that stunned you if you too close to it and we realized fast we did not want to fail any of those saves, so we actually got our Cleric to cast Bless instead of his usual Spirit Guardians, and that tiny bonus really made a difference. I take Resilient on all of my characters, even if it means I can't get a 20 in my important stat (which is why my level 10 Wizard still only has an 18 Int) because there are saves you just don't want to fail, like the above.
And on a long enough timeline, something is going to target one of your bad saves, since most every character has a few of them, and the DC's can eventually get to "cannot save on a 20" in some cases, and all the advantage in the world won't save you.
I've got my DM afraid of Synaptic Static now, because unless they're immune to psychic damage, there's not much his enemies can do about the "muddled thoughts" effect (as I understand it, you can't even negate it with Dispel Magic since it's an instantaneous spell? I think?) and as it's no concentration, it can stack with similar effects like Bane or a source of Disadvantage to just turn off all the low Int monsters.
He doesn't want to nerf it, since it's a 5th-level spell and he feels the power level is appropriate, it's just a bit much. I feel our game will end soon because worse spells are in the future. I could just not take spells like that, but then we encounter enemies like the above blind/stun every turn aura guy who are just that much worse, lol, so I feel like I have to keep things like that locked down if we're going to survive.
It really makes me miss 4e where the individual spells had weaker effects, rarely lasted more than a turn, but could be used more often than these big limited use nukes that are either duds or can turn an encounter inside out.