Why is UX design important for online multi-tenant B2B SaaS application?

I work as medior backend developer in a small company (~ 30 people), where we build an online multi-tenant B2B SaaS application for energy management.

I would describe our app as having many cool features, which are not well presented. The overall UI design is like from 2005, and overall user experience is sometimes confusing even for me, when I should clearly know what's going on in there.

My problem is the following:

• We've developed features that we were told "our customers needed", but I have recently found out that the features are not used by anyone, even after several months.

• Our CEO/Sales person does not want to invest in better UI/UX design because, by his words, "design does not sell in B2B", even though we've never performed any customer satisfaction survey.

• My attempts at gathering user feedback were postponed, because it was "low priority".

• I was told that feedback from our users is not important, because most of them are not the one who pay for the service.

• The only solution provided by management was to enlarge our base of sales people.

So, how would you convince anyone who does not believe that UX design (and design in general) are important, to send a survey to users?

My goal is to perform a survey to get feedback. If the feedback is as bad as I think it will be, and our management still keeps their statement, then I am ready to resign. But I don't want to give up yet.

I read numerous articles about B2B design, but most of them are about website design available to everyone, so SaaS could differ. Also, I get that it's hard in B2B to reach the right people to gather feedback from.

I would be happy for any suggestions.