Naw, not weird at all, as these things are cyclical.
As I see it, every era/generation has its share of intense periods of competition, regardless of surface.
The same applies to those lull periods as well.
During those lulls, players retire, nurse injuries, experience lengthy recoveries, or the association simply experiences a general changing of the guards.
During some of these periods, when the competition isn't as intense is when breakout players forge ahead and establish themselves, or the current elites improve. In this case, the current elites improved.
It's obvious that both Serena and Sharapova have put in practice time to hone their clay court skills.
It's what champions do (constantly think of improving).
Why wouldn't this include the clay surface, and why would it be considered weird?
Serena and Sharapova just happen to be two players who have weathered the times and forged ahead.
Who says players have to possess excellent clay court technique to experience clay court success?
Both possess styles that do well on most surfaces anyway, and their clay court techniques are good enough to defeat even the so-called expert/career dirt-ballers.
So 'no', not weird at all.
I recall reading an article around the time Serena turned pro, where Serena mentioned that she practices mostly on clay courts at home, IIRC.
Do any other Serena fans out there recall this article, or Serena saying this?