I don't really see it improving stunning strike much since it's limited to 1/turn.
This is why it is so attractive for the extra attack. You stun one enemy with an attack (often at range by throwing a dagger) and you still get your full complement of other attacks on another enemy, usually the enemy who the party is concentrating on.
It is a control element and I see it in play all the time
To put this another way: What if I gave you a half feat that let you try to stun an enemy whenever you take the attack action without using up any of your attacks. That would be a pretty good feat and that is essentially what this does and it does damage to boot.
Your first 2-5 attacks probably hit at least once, so you can stunning strike then.
But you are doing two different things -
stunning an enemy (effectively stealing his turn and setting up allies) or on a save giving him half speed and an ally advantage while you are trying to drain the hit points and kill another enemy.
Every attack you use to try to stun one enemy is an attack you can't use to do damage to another enemy.
Stunned is most effective as a Control option and you should generally concentrate on draining the hit points of the enemies that are not being controlled. This is different if you are fighting enemies with a high armor class.
More attacks is still more chances, but diminishing.
Ok here we go, real combat from a recent game during a massive melee:
Shadow Monk is 1V1 on a Frightened Frost giant inside a zone of darkness, our Rogue and Druid who is supporting a Moonbeam are cornered by an Ogre and a Frightened Hill Giant. There are lots of other ogres and a few other Giants, most of them are either frightened due to dragon fear and Beguiling Twist or frightened and fleeing due to the Fear spell, but they are not relevant here.
The Monk attacks the Frost Giant with all 5 attacks and then uses nick to fling a dagger across the room (both long range and ranged attack in melee but throwing it from inside darkness so no disadvantage). Hits the Ogre and uses stunning strike on him. Now the Ogre loses his turn and is not a threat to the Druid. While he is stunned, the Ranger (me

) uses an attack to throw a net on him with an automatic save fail, basically making him lose another turn since he has no way to damage the net and has to use an action to free himself.
We also have a Rogue with Elven Accuracy in the party and using stunning strike on whatever enemy the Rogue is going to attack will give the Rogue 3-dice advantage even if the bad guy saves. We did not do that in this case (the Rogue was concentrating on one of the giants), but we do it often.
That doesn't include the accuracy and AC buff.
Or taking +1 Dex and +1 Wis/Con.
It does include the accuracy and AC buff as long as you have an odd dexterity and taking +1 Dex, +1 Wisdom for better AC only works if you have a odd score in both of those. +1 Constitution is a waste on a Monk IMO, again your constitution would need to be odd in addition to Dex and even in this case +3.5 damage and another attack at 4th level beats 4 more hit points by a wide margin.
There are times an ASI will work out better if you roll ability scores and manage odd Dex and Wisdom. On Standard Array the only way to get odd Wisdom and Dex on a Monk is with 17Dex/15Wisdom or 15Dex/15Wis after species bonuses, which is really bad generally. On point buy there may be some builds that offer that, but generally I think the optimal for point buy is 17/16 and a half feat.