But haven't these jets sustained this tempo for over 2 years now?
We don't know that. He didn't say anything about it being sustained long-term.
Russia has no clear air superiority over Ukrainian skies so the strike missions couldn't have been too often.
But we know what the Flanker (and by extension, Fullback) platform is capable of. We know that 4+ sorties per day can only be achieved during surge ops.