Playing next to either Fred or McT means Pog and the other guy get 50/50 distribution of defensive work.
Like last season, post lockdown, when Matic was in decent form, we didn't really struggle with Pog playing along side him. Similarly, In Mou's 1st season, Pog played alongside Herrera with Mata/Mkhi, Rashford.d/martial, Rooney playing ahead.
I'm not expecting Rice to do all the defensive work, but the 1.5x of the work that McT and Fred do can be done by a single natural DM
Last season after lockdown every team we played was either fighting relegation or in terrible form. Even so we only really played well for the first few of those games, and then for the rest of them we were struggling through while playing quite average. In fact the only decent team in good form we faced after lockdown was Sevilla in the EL, where we dropped Matic and played Fred instead. Interestingly the midfield worked better in that game than it had for the previous month or so, but our attackers and defenders poor performances ended up getting us knocked out.
In Mourinho's first season Herrera and Pogba only played as a midfield duo 6 times in the league, for 3 wins and 3 draws. Our best form of the season came when we bought Carrick back in next to Herrera and pushed Pogba further forward. Fellaini also played regularly with them.
Throughout his entire time here Pogba has struggled for consistency and has cost us defensively when played in the deeper position. Most people have put that firmly on Pogba himself, but many of us have said right from the beginning that he simply isn't suited for that role.
Fred does more defensive work than just about any midfielder in the league other than Ndidi and Kante (and he's only just behind them). Rice will do less defensive work than Fred does. What Rice would do is help protect the centre of our defence better, but on the flip side we'll be less likely to quickly win the ball back high up the field so the opposition will find it easier to keep the ball and build their own attacks. In reality if we do sign Rice I expect we would end up regularly playing Fred-Rice (Fried Rice?
) together, which should be an improvement over the current McFred combo but still doesn't have the ball-playing ability that most would want. We'd then have to spend more money on a second midfielder to get that balance right, but that midfielder would have to be solid defensively in his own right.