Define 'rather rare' Put a number to it.
Well, do YOU have a statistic indicating arson represents a sizeable part of the incidents ? Because me, I don't.
What I know is that arson cases are almost-automatically covered by the media, and over the next 12 months I only remember two cases : one of a school, the other a synagogue. Let's suppose there were three times as many cases as I've seen, that means we talk about 6 to 10 arson cases. Since 183 antisemitic acts have been monitored, we're talking 3 to 6% of the total cases. Which is still rather rare, as a percentile.