This snapshot can tell multiple different stories at the same time.
Story 1: Numerous elite, highly paid RBs of the past 10 years (as well as other eras) are not well-represented in Super Bowl champions. No Adrian Peterson, no Derrick Henry, Dalvin Cook, no Alvin Kamara, etc. Historically, Emmitt Smith and Marshall Faulk are the only Salary Cap Era counterexamples I can find.
Story 2: good running backs who alter the way a defense has to play are a key ingredient in getting to, and winning a Super Bowl. Besides Lynch, "Playoff Lenny" Fournette, Legarette Blount, and even Sony Michel had dominating performances and/or game changing plays on the way to getting a Lombardi. (Sony Michel had impressive 2018 playoff performances)
Story 3: While highly capable running backs are a huge asset in winning a Lombardi in the NFL Salary Cap era, "highly paid" running backs are not.
You may want to think twice about sliding a ton of money to a running back
www.cbssports.com
Story 4: The career paths of the running backs that played a pivotal role in Super Bowl wins are very checkered, and highly paid, high-drafted running backs are usually NOT an ingredient of Super Bowl winners. Most often, the big-time playoff and Super Bowl performances are NOT with the team that originally drafted them, with Sony Michel being the lone recent exception. CJ Anderson of the Broncos was an UDFA signing for them. LeGarrette Blount was an UDFA due to personal/behavioral issues. The Patriots have had amazing success with RBs picked up off the scrap heap, as well as mid-rounders like James White. The Seahawks acquired an unhappy and under-utilized Marshawn Lynch via trade. Also, many top RB performances in the playoffs and Super Bowl were by running backs who got their shot as the feature back simply because they were the most healthy and capable option available at playoff time.
Summary: Teams need to have at least one really good, but not necessarily elite, AVAILABLE running back to win playoff games and Super Bowls. Running backs get injured a lot, and more workload = more injuries. Teams need to either have multiple "really good" running backs or have "good luck" with RB injuries to have at least one "really good" RB available at playoff time.
Conclusion: The Seahawks absolutely should draft Bijian Robinson IF the draft board falls their way, despite already having the excellent WalkerIII. Robinson will be a better-than-really-good running back, and should provide 4 excellent years on a rookie contract that does not break the salary cap. His talent will be a playoff-game difference-maker. If Seahawks don't draft Bijian? They need to have a stroke of luck in a mid-late-round/UDFA pickup, or great luck with a a reclamation project off the scrap heap.