Rielly, for what he has shown himself to be, is only capable of so much on his own. When you stop and look at it, it's actually pretty surprising to see some of the successful seasons that he has had under the circumstances. If you're not sure what I mean by that, just take a brief glimpse at some of the names Rielly has been paired with during his NHL career.
Rielly is not only a gentleman, but a true professional, so he wouldn't come out and publicly admit that he's frustrated with the quality of D partners he's received during the NHL career, but he must be grinning from ear to ear knowing that he and Tanev will have the opportunity to play together in 2024-25.
Tanev, like Brodie, is never going to dominate on the scoresheet, but he provides a stable body back there, who is effective in all 3 zones and possesses a solid transition game. Since Rielly did have his good stretches with Brodie, I'd imagine that playing with a better version of Brodie will lead to the best Morgan Rielly we've seen yet.
Obviously, until we see the pair together on the ice, this is all hypothetical, but I'd be inclined to believe that, as long as he and Tanev can stay healthy and find some chemistry early, Rielly could be in for a career year.