The SaaS application can either be developed from template building websites like WordPress or through scratch. Yes, it is right, WordPress can be used to create a SaaS solution.
However, some of the best SaaS Application platforms are the one through which people will get a SaaS product developed, they have to pay attention to all the requirements. If the enterprise want a SaaS product which are properly customized then they need to try to develop it from scratch. The main thing to look for is the requirements.