You were asking about gates for LGA and DTW at BOS, so I guessed that you were connecting through LGA in one direction and DTW in the other. I'm sorry to hear that you felt it necessary to cancel the trip.

Perhaps you can plan a trip soon with the airports chosen strategically to minimize walking. From PIT this is harder because most places (except hubs of course) require connections on DL. DTW is normally pretty good if the red train is working.

LAX is good and so is MEM but I'm not sure they're served from PIT.

MSP is good due to the electric carts, although it's a long walk to the light rail station.
At MSP the major car rental agencies are in the "terminal" meaning in the back of the parking garage attached to the terminal, but there's a little train in the basement or you can take a cart to the airside C/G connector path at the back of the parking garage and exit at the skyway security checkpoint to be just an elevator ride away from the rental car counters.

DCA is good in terms of the walk to the curb (and farther to the metro) but the last time I rented a car there, one could either wait for the airport shuttle or walk to Hertz in the fare part of a short term airport garage.

LGA normally isn't that bad, but current construction is kicking people to first use a shuttle to the old marine terminal and then get further local transportation, at times including uber/lyft.

Maybe look for a MSP connection (and plan to use the electric cart) to a small airport where it's a short walk from the gate to the curb? What would be fun and a legal routing from PIT? AUS? MSY? LEX and the bourbon trail? Maybe SAT (but I don't know that airport and it's getting into the hot and humid season)? COS if you can avoid a DEN connection?