Red Bull's Max Verstappen is third overall, 30 points off the lead.
Asked whether they could see a scenario where Hamilton might not be champion at the end of the year, Vettel and Leclerc agreed it was unlikely.
"I think (only) if Valtteri wins the championship," said the German, himself a four-times world champion.
"I think Lewis is obviously the main contender," added Leclerc. "The only one that could probably stop him doing that is Valtteri."
Mercedes, winners of the past six drivers' and constructors' championships, have started 2020 with three wins and three poles and are 66 points clear of closest rivals Red Bull.
Hamilton, fourth in the opener at the Red Bull Ring, has won two in a row and the next races are at his home Silverstone circuit.
Bottas has a win, a second place and a third -- in that order -- and blew Sunday's race at the start. The Finn started stronger last season and still ended up far behind his team mate by the end.
The only others on the podium have been Leclerc, McLaren's Lando Norris and Verstappen -- the first two both failing to score on Sunday.
Mercedes have responded with fighting talk to those who suggest the championship is already sewn up, with team boss Toto Wolff and technical head James Allison warning against complacency.
"I'm not sure I'm seeing the competition fall apart," commented Wolff on Sunday night. "We can see that Red Bull was struggling all through the weekend and then they had a pretty decent race car.
"It's 30 points after three races that we have with Lewis to Max. If you have one DNF (non-finish) the gap is gone."
The evidence suggests Mercedes are on another level, however.
Hamilton lapped all but three cars behind him before his final pitstop in Hungary and was still nearly a minute clear of fourth-placed Lance Stroll in a Racing Point that is basically a copy of last year's Mercedes.
While the Briton saw no danger of the championship becoming a procession, he said he would like more of a fight.
"I think the Red Bulls have been doing a great job and I'm sure at some stage they're going to make some improvements as we get into the season," he said.
"I'm hopeful we will still find some challenges up ahead."
(Reporting by Alan Baldwin, editing by Christian Radnedge) ((email@example.com; +442075427933;))