The hit rate on day 2 RBs (i.e. Swift/Akers/Dobbins) doesn't justify giving up a bird-in-hand young star WR like Moore, JuJu, or AJB except in leagues with extremely skewed formats that lend artificial value to the RB position. There are 4-5 RBs this good in every draft class. They aren't a special commodity.
The idea that "they'll carry value a year from now even if they don't hit long-term" is built on the hypothetical reality where you can always recognize the hits from the misses and sell accordingly, but that's not how things typically work in practice. If you burned a top 5 rookie pick on a back like Kevin Jones, Julius Jones, Anthony Thomas, or Doug Martin who peaked as a rookie, it's pretty likely that you would've bought into the hype after his big rookie year and held the bomb while it exploded on your roster. Most people don't cash out when their young RBs show promise. I don't see Miles Sanders or Josh Jacobs owners desperate to make deals right now. If you draft someone like Swift and he ends up being a long-term mediocrity, there's a pretty good chance that you'll be the one stuck with him.
3/5 of my leagues are very flex-y with only 1 mandatory RB spot, so maybe that colors my perspective some, but I'm definitely not itching to trade my rookie draft hits like Deebo and JuJu for a Cam Akers who's probably a 30% chance to become Ray Rice/40% chance to become Zac Stacy/30% chance to become Kenny Irons. I don't believe the math supports that move, and if I were desperate for RB help then there are numerous alternatives I can explore (pay a premium for an elite back, pay less for an aging veteran, or buy a cheaper prospect). I'd rather make a big play for a Mixon, go the short-term rental route with a Henry/Gordon/Drake type, or make a bargain play for a D Harris/Edmonds/Mattison than sell off top 10-15 dynasty WRs for an average day two RB talent.
If your league format makes it logical to sell off your best young players for mediocre rookie prospects at another position, your league format is pretty imbalanced.