Comparing the context behind Rooney's arrival in 2004 and any potential Sesko signing now, there are a few similarities that I can see. RVN then and Ronaldo now are established albeit there are obvious signs of decline and oversized self-entitlement. Saha then and Martial now have the same probem - INJURIES! Smith then and Rashford now will try, but the end product can be difficult to find a number of times.
I know that people are worried about the possibility of Sesko leading the line too early if Martial gets injured AND something just does not click with Ronaldo (vis-à-vis Ten Hag's plans and tactics), but it is a risk that everyone must take. Wayne Rooney was also thrown in that situation when Ruud began to get injured more often while Saha/Smith had problems firing their way through as well. It's about thinking ahead of time and seeing what the kid is made of rather than focusing just on short term.