It’s missing a comma. “If a company offered these customer solutions on their website, which would you prefer**,** assuming each was equally capable of providing a resolution to your issue?”
The actual main question is just “Which would you prefer?” Then it has two modifying clauses: “If a company offered these customer solutions on their website” and “assuming each was equally capable of providing a resolution to your issue.”
It seems like they overloaded the question with qualifiers to get the type of answer they want. I would have just said. “A company offers the following solutions on their website. Which would you prefer?” If I needed the extra clause, I would write it in parentheses afterwards: “(Assume each option is equally capable of resolving your issue.)”
This is actually a concern I use when I am writing my posts here. (In fact, I just did it right now.) I am aware that too many clauses can make written speech harder to follow. If I just wrote my inner monologue, my writing would be much more full of clauses.