Were Saiyans really meant to be the strongest? They don't sound all too different from Namekians on average. As a child, Gohan was thought to be a prodigy with a Battle Power of 710. Vegeta, who was the greatest prodigy among Saiyans amounted to far less than Nail after a lifetime of battling on Freeza's behalf. If we look at an average Saiyan like Raditz, he was far outclassed by the average Namekian warrior. Saiyans might have produced more prodigies than Namekians, but on average the Namekian race may have been stronger. I'd say their potential was pretty comparable overall.
I don't think it's suspicious really. Goku and Vegeta were both close to becoming Super Saiyans by the end of Namek, so it makes sense that their Zenkais would push them to such levels. Their Base levels stalled out after that allowing Piccolo to catch up. Hell, Piccolo had arguably caught up to Vegeta by the time Mecha Freeza arrived, and that was solely by training on his own.