"Last year ... the bench OPS+ was 78 for Heredia, 57 for Motter, 37 for Leonys, etc." Maybe that was what Valle was mostly thinking about, being freshest in memory (and horrible even there).
At Slack, Lampoon writes:
the other day Dave Valle was remarking on the importance of bench players in a "chain is only as strong as the weakest link" sort of way.
As I recall, he said there would be about 15 games in which the performance of bench players would be critical to the outcome. Where the margin between playoffs, or not, is about 1-3 games. When the benches play there can't be a big drop-off. Is that a reasonable analysis?
Bill James' approach to this would be to study all playoff teams who ever made the postseason, and to compare their benches to non-playoff teams' benches. That would be a study that would put "paid" to the question. I'm guessing the playoff teams would show considerably better performance than the non-playoff teams.
Lacking that kind of data, I can offer my own observation over the last 40 years ...
The 1975 Reds won 108 games with very poor production out of their bench. Dreissen had (only) 210 AB's with a 125 OPS+, but their other benchies were 49, 59, 86 and so forth. Also their starting pitchers included ERA+'s of 88, 97, 77, etc. It's true they did have four good relievers that Anderson would go to early in the game. Behind those relievers they didn't have much to talk about.
So the famous 8 starters in the Big Red Machine all had AB's from 463 to 662. There were no significant injuries and so they cruised to an easy playoff spot, put the Big 8 out there in the playoffs and simply mulched everybody. The starters did it all. I'm sure you could find many, many Yankees teams from 1921-1964 that were similar. If you get a set of stars playing together who are healthy, your bench just isn't going to matter much.
On the other hand, the Astros, Indians and Yankees (+200 runs) last year had strong benches. The Astros for example had Marwin Gonzalez, Evan Gattis, and several others rack up 100+ OPS+. They had a deeeeeeep organization.
To me it really boils down to, your bench can't KILL you, if your starters are not playing 150 games. Last year the Mariners saw Haniger get hurt and only play 96 hamstrung games; Juan "sudden" Segura got hurt and missed 40 games, Dyson played only 111 games ... and the bench OPS+ was 78 for Heredia, 57 for Motter, 37 for Leonys, etc.
And of course we won't even talk about the pitching, which plowed through 40 pitchers (Felix 86 IP, Paxton 136 IP, Smyly out, Iwakuma 31 IP, etc) and there were plenty of guys who started games and provided ERA's of 5.57, such as Casey Lawrence.
the 2017 M's were a perfect example of a team whose (excellent) starters got hurt, and the (lousy) bench behind them crashed and burned.
The bottom line is that the Mariners have a fearsome starting 9 and the bench is going to come into play if and when these guys get hurt. If Jean Segura or Robinson Cano get hurt, how well can Andrew Romine fill in? Probably not very well.
The M's do have a number of players with a history of playing 150+ games. Cano of course, Boomstick as DH, Zuumball's been healthy, Seager is a metronome, Gordon has 145+ games in 3 of the last 4 seasons, the OF has 5-to-make 3, etc.
If the M's top 4 starters go 180 IP each, and the starters are healthy, they look like a major contender to me. Of course that's axing a lot :- )
When Mark McLemore & Stan Javier makes your front 9 super good because none of them are tired... The current rendition of the M's don't have that available as a benefit.
during my Sunday stat journeys. McLemore had 70.1 innings at SS in 1289 MLB games before Gillick picked him up that year. He hadn't even had more than 21 games there in a minors season since he was 18 in Peoria when it was a California affiliate. Then Piniella puts him out there for 262, 2 and 304 innings the next 3 years and I recall him being pretty decent. FG has him for 4 TZ in 2001 and 0.7 UZR in 2003, both stats blank for the other year.
Javier hit so well that year. Our ceilings at those spots seem unattainable in comparison. Most other positions on the entire roster the ceilings now are higher than they were to start that year.