Yeah, it is strange. Thing is, Vegeta's other statements gives me the impression that he considered his Super Saiyan to be in a class of its own.
Vegeta: “There’s no need for us to wait for Kakarot! Maybe you can’t tell, but I’ve become a Super Saiyan. As long as we’re both Super Saiyans, I the prince will definitely be several levels stronger than a guy like him…!”
Vegeta: “I-I’m the prince ,the most elite of the Saiyans…Now that I’ve become a Super Saiyan, I should be #1 in the entire universe…Is it because my opponents are androids…Is this my limit?...”
The same Vegeta has no issue disregarding Trunks' power when it comes to challenging the Androids:
Vegeta: “Looks like that level [of attack] is just a waste of energy.”
Vegeta: “What an absolutely annoying bunch…Do you really think this is an opponent you guys would be any use against?”
So based on the above, Vegeta thinks the Androids>Super Saiyan Trunks since he doesn't think he'd be of any use against them.
Then you have to ask yourself this question: is Vegeta more salty that the Androids/Piccolo/Cell have greater power than himself as a Super Saiyan rather than the "Super Saiyans" as a whole? I'd say so. Vegeta considered himself #1 above everyone, but he had no issue assuming the Androids were too strong for someone like Trunks, who was also a Super Saiyan. Maybe Goku as well.
With that, we know the "Super Saiyan" can't be referring to a certain wall of power. If it was, everything stops making sense.
As for Vegeta not saying anything about Piccolo, I'd assume he didn't care because Piccolo wasn't stronger than himself. I don't think Vegeta really cared about "Super Saiyan" amongst all the Saiyans. Only himself, since he thinks his title would automatically make his Super Saiyan more powerful than the others.
You could also go with the idea of Vegeta not caring because "Super Saiyan" was still the strongest in general.
Like, if Super Saiyan was originally a 20 max, but further improvement took it around 60-70, I don't think Vegeta would take note of someone jumping to 30 or 40 because the Super Saiyan would
still be well above that newer power (Piccolo) that surpassed the old highest (Super Saiyan Goku/Trunks) level. I hope that makes sense.