He's about to be 26 and has a career high of 15 points. For whatever reason, he's never been able to establish himself as a quality third liner, let alone a quality second liner. He has exactly 8 career playoff games with more than 13 minutes time on ice. He has exactly 4 playoff games with more than 14 minutes time on ice. His playoff Corsi is poor in both 19-20 and 20-21. It was solid all the way back in 18-19.
His ppg this year was 0.29 before he was injured. Our third line, now that we have a decent third line, averages 0.33 ppg, 0.40 ppg, and 0.68 ppg. Our fourth line averages 0.25 ppg, 0.31 ppg, and 0.13 ppg (the last one being Brodzinski).
Blais is a plus fourth liner, and a middle of the road (if not low-end) third liner. Always has been and likely always will be.
I certainly wouldn't put him on our third line over anyone on it now and it's only getting worse in comparison for Blais when Kakko returns.
I think you are overselling his value to a team because Chris Drury traded Pavel Buchnevich for him.