To be fair every champion in more than a decade has put in such performances. Arguably Russell himself put in such a performance on Saturday.
Sadly Sunday showed why Russell isn't yet the man to replace Hamilton, but he's shown plenty to suggest he might become one. He wouldn't yet directly threaten Hamilton over a season (Hamilton's consistency is his biggest weapon now, not his speed), and Mercedes had enough in hand in 2020 and almost certainly 2021 to risk Hamilton vs a potential successor without losing out to Red Bull.
Presumably Mercedes only signed Bottas as they've received assurances that Hamilton will sign on for another couple of years, but if Hamilton were to unexpectedly switch to Ferrari to fulfil the dream that Senna never got the chance to, or retire, that would leave them in a potentially sticky situation. Is Bottas enough to win? Who else would they get at short notice to do the job? I suppose Vettel's very public availability gives Mercedes a little leverage in those discussions; I doubt they would have signed Bottas before Hamilton if Vettel wasn't on the market.