Russell pulled off an unlikely victory on the road having decided mid-race to stick with the tyres he fitted on lap 10, rather than stop again.
The decision leapt him up from fifth to the lead, from where he defended his position against Hamilton’s attacks in the closing laps.
McLaren’s Oscar Piastri also finished right on the Mercedes’ tails in third place.
Sholvin admitted the lower weight would have given Russell a performance advantage.
“In terms of pace at the start of the race, it is nil because George’s car and Lewis’ car start the race at the same weight,” he said.
“Obviously, as George’s car was losing weight faster than Lewis’ throughout the race, there is an associated gain with that.
“But you are into the hundredths of a second per lap. It will be very small because when you are talking about amounts like one or two kilos, they do not amount to a lot of lap time.”
Shovlin said the outcome of the race was “bittersweet” for Mercedes because Hamilton had still managed to win after the team had looked uncompetitive in Friday practice.
Mercedes tried a new floor design on Friday at Spa but took it off both cars for qualifying and the race after their difficult day’s running.
But Shovlin said it was likely the new floor would be used again at the next race – the Dutch Grand Prix on 23-25 August.
“We are planning to do that,” he said. “The reason we reverted the car to the Silverstone spec on Friday night was because we had a good race in Silverstone.
“Spa and Silverstone are not dramatically different circuits in terms of the corner speed range that you are dealing with.
“We had clearly introduced some problems somewhere. We think that was largely due to how we were running the car in Spa, not induced by the updates themselves.
“That was giving us a bit of bouncing in the high-speed corners, as well as a few issues with the balance.
“Going to that Silverstone car got it all back to normal. We have since had time to look at the data to understand what it was that we did, and we are pretty confident that we will be going for a reintroduction in Zandvoort.”
