Sometimes sports analogies are appropriate, and do not belie the seriousness of the underlying issue.
Say that it’s necessary to have a group of baseball teams play a set number of games every week.
Initially, each week is covered with 4 teams of 9 players. That’s 36 players in total. At some point, it’s decided to move to a three-team structure. Now, there are 3 teams of 12 players, but still only 9 players can be in the lineup at any one time.
Though not necessarily in any one week, over the long run, everyone’s playing time will stay the same, because on the 3-team plan, 3 players have to sit out every 4th game (we’ll assume a coach who is scrupulous about keeping everyone’s playing time equal) because, again, only 9 players can be on the field at one time.
In the three team structure, there is now an added possibility of using a DH every game, i.e. using 10 players in the lineup at one time, in which case the total amount of playing time needed to fill a given week would increase.
The non-analogy version of this is to point out, whether you have 3 platoons or 4, that if the number of firefighters on a shift doesn’t change, because the number of hours in a week doesn’t change, the number of hours worked across the department as a whole stays the same. Total hours can only increase, if the number of firefighters per shift increases.
So what’s the Mayor of Providence’s actual plan for the fire department?