No — the theme only describes the art and story, not the mechanics. Medieval slots on this site come from Twist Gaming, Triple Cherry, each with its own RTP, volatility, and bonus features, so it's worth checking a game's own stats rather than assuming from the theme alone.
Pixel Castle by Twist Gaming has the highest published RTP among medieval slots on this site, at 97%. Not every game in this theme has a published RTP, so this reflects what's actually disclosed, not the full set.