Nelson Cruz had an on base percentage of .397 last year. Arraez had an OBP of .364. Donaldson had an OBP of .373. If you're looking for a skill set to equate to runs, it's not going to be on base percentage, at least not entirely. You need to look at the extra base hits. A guy who gets on base at a 40% clip but only gets singles is probably going to score fewer runs than a guy who piles up doubles and HR but only gets on base at a .330 rate. Last year, Sano, Donaldson, Rosario, Buxton, Kepler, Cruz, Cave and Jeffers all scored more runs per plate appearance than Arraez.