Sintzu you make Vegeta sound better off than he really is by only looking at it from just the one side.
Or in the Freeza saga when he was beating Freeza's men left and right?
He was beating up C list characters, henchmen like Cui, Dodoria, Guldo and Zarbon (who also beat him). He was scared shitless both when the Ginyu Squad and Frieza showed up, got his ass handed to him by Recoom and Frieza twice. Had he beaten Captain Ginyu that would have been something but no he just beat up Jeice who Goku had already beat.
Or in the Cell saga when he saved Goku from #19 and help Gohan beat Cell?
Piccolo could have saved Goku if he had to. He "helped" Gohan beat Cell after it was already his fault that Gohan was injured preventing him from beating Cell much easier. He killed the weakest android and then proceeded to lose against #18, Cell, have a rough time against the Cell Jr and then was almost killed by Cell again.
Or in the Buu saga when he was the only Z fighter standing alongside Goku in the final battle?
This was just down to sheer luck. He was dead throughout most of the saga after again losing to Buu and then was brought back after everyone else was already dead and would have died again had Goku not teleported him away and then again was losing to Buu.
Or in BOG when he was the only saiyan that was able to do anything to Beerus without ssjg?
He didn't do anything, he snapped and wailed on Beerus to no effect at all only to then get beaten like a chump.
He's a great character but he is pretty much useless and can hardly ever beat anyone that shows up.