We were not shown what Piccolo told everyone, but it's likely he said the same things Trunks said. Here are the rumors about the Androids:
Chapter: 335 (DBZ 141), P2.3
Trunks: “3 years from this current era, on May 12th around 10:00 AM, a terrifying pair will appear on an island 9 kilometers to the southwest of South City…Monsters with tremendous power unlike anything in this world…”
Chapter: 335 (DBZ 141), P3.3-4
Goku: “For you, a Super Saiyan who instantly defeated Freeza and co., to call them monsters is really something…
Trunks “Yes…I’ve stood against them, but unfortunately…In any case, I’m up against two of them…Even fighting one-on-one, I could barely manage to escape…”
According to the rumors they were beasts, they could absolutely wreck Trunks even if it's 1v1. The Z Fighters knew the floor of what the androids could be, at the very least they are above Trunks. They expected something between Yardrat Goku to > Android Goku. Here is what Vegeta said about 19:
Chapter 343 (DBZ 149), P7.4
Vegeta: “I’ve realized by watching your faint movements up to now…That you guys don’t seem as terrible as the rumors made out.”
To Vegeta, 19 isn't as strong as the rumors. He doesn't even get to be Yardrat Goku level, he is completely out of the Expected Androids tier. 19 likely is still around Trunks though, considering both Vegeta's statement not putting him lower (He says 19 isn't as fearsome as the rumors, but doesn't deny he's fearsome or call him trash) and his durability feats. I think if 19 could stomp Trunks, Vegeta's coment would be similar to Piccolo's on 20:
Chapter: 347 (DBZ 153), P3.2-3
Piccolo: “It seems that in the original history, we were supposed to be wiped out by you two androids…But it looks like the future has changed somehow…Was it that you weren’t as strong as we thought?...Or have we grown too strong?...
Piccolo admited 20 was up to the rumors ("Have we grown too strong?") but 20 is like the bottom tier of the expected androids. Vegeta would have said something similar if 19 was as strong as Yardrat or Sick Goku.
It was actually suggested Sick Goku's stamina was affecting his perfomance. Tenshinhan noted he was really out of breath after flying to the island:
Chapter 340 (DBZ 146), P7.5
Context: after Goku and co. fly to an uninhabited location
Tenshinhan: “Wh-what’s going on? Son’s out of breath…He merely flew here, so why…?”
So obviously those stamina issues should carry to Super Saiyan and even get worse, considering how the Super Saiyan puts strain on the body according to Vegeta: