If your competitor has a clunky non mobile website do you think potential clients are going to want to visit that website? I think not. If your website is mobile-friendly intuitive responsive as up-to-date content and is thoughtfully laid out resent the information in a logical manner with great functionality, you just took a potential client from a competitor and made them yours.
Think about it this way. When you are on your phone searching for a service, or a product, (and more than 50% of users use their phone for this), and you find what you want, and go to the website, and it is clunky. It loads slow. Total buzz kill. What do you do then? You go to the next listing and click on that. That site is fast. intuitively designed, easy to use, and super easy to navigate. There is one word for that. SOLD.
What happened in that entire transaction is because of the website. Brand A has the same product as Brand B, Brand B’s price might even be a little higher. Brand A’s website sucks, but Brand B’s website makes things much easier. You will buy Brand B’s product. You shouldn’t have to bed for the a company to take your credit card.