Kinda hard for other WRs to step up when Stafford's primary read is Kupp. We have seen Matt ignore other open receivers to force feed Cooper. I have no problem with this except that it doesn't develop the level of trust and timing with Stafford and the other WRs that is necessary for them to "step up".
Jefferson and Nacua provide the Rams with two good WRs. Jefferson is a bonafide deep threat with Nacua as a short to midrange possession threat. Whether Atwell, and Robinson can fill the 3rd WR void remains to be seen. But until they do I think we will see more 12 personnel. Higbee and Hopkins/Allen aren't TEs to ignore. What will change is the nature of McVay's passing offense. I think in the short run it will be run heavy and possession passing heavy. Moving the chains is nothing to scoff at. As we saw in KC, that approach limits the opposition's possessions and if you can get a lead, it changes how they must play their offense.
The deep strike potential will still be there with Jefferson and Atwell, but I think the emphasis will change until Kupp returns. This is something the Rams need to sort out because the likelihood that Stafford, Donald and Kupp being gone in 2025 is very high.
Robinson is 6'1" and runs a 4.59 (Kupp timed at 4.6 as a rookie) which is decent speed for a man his size. That said he has good agility, but he's no Kupp in the way he runs his routes. Thus far in his career he's a good WR not a great WR.
The way this WR group is built it would seem to be one that isn't so much a vertical threat but one that can certainly get chunk yardage, i.e. 15-25 yds. I think next year the Rams will grab a QB and WR, with length and speed. Thats why it wouldn't surprise me if the Ram's 3 primary WRs are Jefferson, Nacua and Robinson until Cooper returns. But from what they are saying Kupp could be out an extended number of games.