Mercedes, distant runners-up to McLaren last year, looked immediately strong in a shakedown test with plenty of mileage last week, and Russell recognised the W17 car was ticking all the right boxes.
While clearly happy with how things were shaping up, the Briton said Red Bull, who have taken the huge challenge of building their own power unit after splitting from Honda, had also stood out.
"We've been quite surprised by what we've seen from some of our rivals, especially on the Red Bull power unit side that looks very impressive," he told reporters before his team's season launch online.
"So kudos to them. We've had a very reliable test but we'll have to wait and see if the car lives up to the expectation."
Mercedes team principal Toto Wolff, clearly reassured but trying to rein in too much optimism at such an early stage, put it more bluntly.
"Obviously you wake up with more of a smile if the car is quick and the early indications that we had were positive -- that at least it doesn't look like a turd and we're (in the) midfield," said the Austrian.
"It looks like we have something that you can build upon."
Ready for title fight
British bookmakers have established Russell as their title favourite, ahead of McLaren's defending champion Lando Norris, but Russell was not letting that get to his head.
"I don't really feel anything from hearing that," he said. "As I've said for a long time, I feel ready to fight for a world championship.
"Whether we have that comment above us or not, that does not change my approach one single bit."
Verstappen missed out on a fifth successive title by two points last year and the uncertainty surrounding Red Bull's engine has weighed on the Dutch driver's prospects for 2026.
With champions McLaren having a Mercedes engine, which is expected to set the standard in a new rules era, there has also been talk of the fight being between those teams.
"It seems like the other power unit manufacturers have done a good job and we know that Red Bull have always had an amazing car," Russell said.
"Even through the years of dominance of Mercedes, it was their engine that was letting them down, not their car, and we obviously know how good Max is.
"I think he's very much going to be in the fight this year...you obviously wish you'd have a slightly easier time of it, but it should never be easy and if you're going to win you want to have fought for it and won it fair and square on track."
Mercedes have an unchanged line-up with race-winner Russell partnered by Italian Kimi Antonelli, no longer a rookie and expected to move up a gear, while Danish driver Frederik Vesti takes the reserve role.
The season starts in Australia on March 8th.