Red Bull's Helmut Marko says that Dany Kvyat just wasn't fast enough to put pressure on Daniel Ricciardo, adding that Max Verstappen is a much better team mate to the Aussie.
Early last year, before the European F1 season got underway in Spain, Kvyat was demoted to Toro Rosso while Verstappen stepped up to the senior bull outfit.
"Daniil Kvyat could not push Ricciardo as hard as Verstappen," Marko told Sport Bild, justifying last year's driver swap.
"Daniel had to learn how to deal with that but we've seen him get faster the more he was pushed," Marko added.
The Austrian also believes the Ricciardo-Verstappen relationship will be kept in check by Red Bull, with no fears that on-track battles will deteriorate into a Senna-Prost-like feud.
"A healthy rivalry on the track is the best thing that can happen to a team," said Marko.
"But so far the competitive situation has not affected them in their work or privately. The two respect each other completely."
Commenting on red Bull Racing's pre-season form, Marko believes Ferrari can challenge Mercedes at the outset but Red Bull will fight to make it a three-way battle.
"Mercedes is still the favourite," he said, "because the engine will still be the decisive factor.
"Renault is making progress in steps. The first will be in Barcelona when we get the second stage of development."
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