It seems odd to me to need to soft start a 2 hp motor. perhaps some of the line disturbance is related to undersized conductors?
Having a soft-starter on any water pump is a good idea, no matter what size we are talking about.
Not so much from an electrical perspective, but from a mechanical one, soft-starters minimise the initial pressure surge created by direct-on-line or even star-delta starters.
I've lost count the number of times I've turned up to faults calls in dairy sheds where couplings have literally blown apart in water lines, this is caused by the hammering effect of running a pump motor up far too fast and the surge of water caused by it.
Using a soft starter is also kinder on the pump impeller to a degree as well.