That is simply one component. From the batteries to the inverter and out to the pump is a lot of things that must work together to deliver the most available power. I am trying to be generous here but you seem to have made up your mind that the problem is your inverter. My test showed that a HF inverter of lesser rating than your SolArk could start a 1/2hp pump under pressure and operate it without problems.The inverter is a Sol-Ark 5K
Designing a good electrical system requires understanding all the parts.