We are talking playoffs not regular season.
We have 5 days off, play 2, have another day off, play 2, have another day off, play 1 and have another day off. That does not happen in the regular season.
11 pitchers has happened in the playoffs several times in the last decade for precisely the schedule shown above. For God's sake, the Sox went with 11 last year vs Houston. Not 2 decades ago. Last year! Not only did we go with 14 positional players, we left Chris Young off the roster!
Guess what? We weren't the only team to go with 11 in last year's playoffs: the Cubs did, too.
I think the Mets went with 11 in 2015. I'm sure there were more.
The playoffs are different. There is no 5th starter needed and more days off than at any time during a regular season stretch. It's a 12 man staff without your 5th starter available.