I'm not so sure this is true. Yes, we got that from KK this year, but CFers who can give you 2.5 WAR aren't often available on short terms deals. The only reason KK was is because he came with a ton of risk (injuries, decline, age, etc.). Who else are you signing to play CF? Adam Duvall?
Look at the cost to acquire guys like Harrison Bader, Trent Grisham, etc. Look at what Starlin Marte cost.
I don't think it's a good strategy to suggesting you can simply go sign a great defensive CF with an average bat for $4-5M per WAR like it's no big deal...