Since the introduction of the V6 hybrid era of F1 Mercedes has been the dominant force, winning six double World Championships in a row, largely thanks to the advantage of their power unit manufactured in the Silver Arrows’ Brixworth HPP unit.
Leaving other engine manufacturers Ferrari, Honda and Renault to catch up, something that took a few seasons, but Symonds expected it to take less time to challenge.
"I wouldn’t have anticipated how long it’s taken for the others to catch up," he said speaking at the recent Autosport International Show.
"They have caught up now. I think Mercedes would even say Ferrari have gone ahead. But it surprised me how long that’s taken."
Before Mercedes returned to F1 as a works team in 2010 they had provided engines for years before, with Symonds believing they still had the best engine during the V8 era.
"If ever you go to HPP and Brixworth, you understand why," he added.
"There are so many good people there, so well financed, such good equipment, fantastically strong leadership from Andy Cowell. It doesn’t surprise me now [but] I didn’t anticipate it.
"I think even if you go back to the V8, I think the Mercedes was the strongest engine, and they didn’t always have it in the best chassis when they were really supporting McLaren.
"But as soon as it went into the Brawn, it won a championship. No, I wouldn’t have anticipated it."