My 2015 Outback has a persistent hesitation when accelerating at low speeds on take off. Spent $800 chasing it without resolution. Transmission???
It would help if you told what was done to solve this problem . Are you just throwing parts and have you had a shop look at this vehicle .
Shop replaced motor mounts. Also changed transmission fluid and filter.
Does this car have an electronically controlled throttle? If so it could be just the lag that is quite normal for this type system.
If it seems to not go at first, then really go with a sudden jump, almost to the point of making the car difficult to control in slow speed neighborhood driving, that can be caused by dirty fuel injectors.