Tolkein calls Sauron Morgoth's Greatest Servant - But does he ever really earn that with his actions?

Alright, so there is a great, incredibly well informed community here so let me ask a question that's been bothering me since I finished the Silmarillion. I'll lay out my reasoning for why it's a question as well, so bear with me.

Tolkein states

Among [Melkor's] servants that have names the greatest was that spirit whom the Eldar called Sauron, or Gorthaur the Cruel.

-The Silmarillion, p.28

What exactly does Sauron do in the Silmarillion to earn this distinction? The Dragon Glaurung is far more of a terror to Morgoth's enemies than Sauron. He annihilates whole legions of First Era elves; more or less singlehandedly breaks the siege of Angband and uses his magic stare to mind control/soul crush pretty much anybody he wants to. Not only that but he exhibits significant cunning and is a successful leader of Morgoth's forces in his own right. How is this murder-addicted hyper-dragon not number one? When Morgoth needed to kill Elves dead he went to Glaurung, handing him command in the most critical battle in the war thus far. The result was a victory so one sided and absolute that in an instant the entire dynamic of Middle Earth shifted completely.

It's also a battle where Sauron is conspicuously absent (this is a recurring theme). Not exactly what you'd expect from Morgoth's 'greatest servant'. If he was really that useful you'd think he would have had some role in a battle Morgoth had been preparing for for over 400 years.

Sauron's biggest contributions to his Master's First Age war effort were

1. Hiding from the Valar...twice


2. Effectively begging for mercy when unable to hide.


3. Losing Tol Sirion to an overwhelming army of two people.


4. Messing with the the wrong girl and getting choked out by her talking dog.

Seriously, all joking aside Saurons first era resume is pretty bad. And lets not forget that

everything past the First Age was more or less an afterthought; paling in comparison in terms of magic, power, epicness, etc.

I get that Sauron is the most 'dark-lord-like' and the heir apparent to Morgoth. The only answer I can think of is just that; Sauron is the only one who'd 'pick up the torch' so to speak if Morgoth fell, wheras Glaurung would have probably just found a pile of gold under a mountain somewhere and been content. He needed direction and wouldn't be 'independently' menacing to Middle-Earth in anything but a localized way (a la Smaug).

But Tolkein is talking about Sauron in the context of a servant, not based upon some hypothetical future-dark-lord skill set. I'm fairly sure the thought of being permanently defeated never entered Morgoth's mind and 'being able to take over for him' was never a looked-for qualification in subordinates. The only thing that makes Sauron special is that he seemed to be the only guy who was good enough at hiding/begging to survive Morgoth's fall.

Saurons Dark Lord tenure wasn't exactly Hall of Fame caliber either. Nothing he ever did on his own was ultimately successful and each of his schemes backfired in some way. His plot to destroy Numenor cost him his body; and his attempt to buff himself with the One Ring ultimately led to his end as a force in Middle Earth.

So what am I missing or misinterpreting? Am I looking at this the wrong way?