I think you're both right.
Regulus in that we needed Saka and Rashford on for multiple reasons. The freshness, the ability to carry the ball on the counter, more goal threats, helping push Argentina back as they may not have wanted to push too far forwards leaving so much space for them behind. Bellingham loses the ball but he was surrounded with no support. Rashford and Saka would've been joining him on that counter.
Lash in that once we get the ball, we have someone at the centre of our play who adds composure so that, if we don't get the attack off, we still at least keep possession and buy ourselves a breather.
Rashford, Saka and Mainoo all help in that regard. Maybe one of Garner/Scott/Wharton could've, too.