I agree with you in what, I suppose may seem the obvious point but I think it's a good one, that 19 or so goals from Sarr along with half that many from Larsen or Nketiah or whoever is better overall than just 19 from Sarr.
My concern is that Sarr got goals last year because he was playing centrally most of the time as a sort of inside right, rather than out wide. If Sage switches system to play with wide attackers, something many of us think he should do to get more out of Johnson in particular, and perhaps Pino too, that might mean Sarr has to go wide. From there he would be less of a goal threat. Or, he would have to play centre forward instead of Larsen/Nketiah.
The big factor for me is that not only does Sarr score regularly, he has a fantastic work rate and energy. His goal for Senegal last night shows how dangerous he is on the direct break, even if fed with little more than a simple long ball. We are likely to serve up a good few of those when under pressure, and to have a forward who can make something for himself out of very little is likely to be very useful to use. Larsen and Nketiah both need chances made for them, to some degree anyway. Sarr seems more able to fend for himself. That allows the rest of the team to defend more when required.