Huge gap between Archer and Cole for sure, but the gap between Cole and Salazar is large too.
Salazar has thrown 150+ innings twice in his career and the last time was 2015. Salazar has a much larger injury risk.
Salazar BB% the last two years have been 10.8 and 10% and when being combined with a HR/FB of 12.4%, 12.8%, 16.1% that isn't a good recipe. Especially with Salazar's 39.2% GB% last year. He's got great stuff and strikes out a lot of guys, but his peripherals look more Carl Edwards than starting pitcher.
Cole has a career 22.4% K%, 6.3% BB%, 47.4% GB% and until last year suppressed HRs. He's more consistent, more likely go give you 180+ innings, which to me is more valuable than the extra year that Salazar gives you. It wouldn't shock me if Cole throws more innings the next 2 years than what Salazar throws over the next 3. Plus Cole with the Astros might be Morton on steroids.