No? It should be a 30% raise for them (for the YT Premium family plan slice of viewers). As long as the revenue split percentage stays constant, an x% increase in the total cost will obviously translate to the same x% increase for each split.
Assuming 50% split. Revenue is $10, Youtube gets $5, Creator get $5.
Revenue increases 30% (not what happened but for simplicity).
Revenue is $13, Creator gets $6.50. Increase is ($6.50 - $5.00) = $1.50. $1.50 is what % of $5.00? => 10% of $5.00 = $0.50, therefore 30% of $5.00 = $1.50.