Not every successful person had a mentor, have seen some successful people with flourishing business and they did it all by themselves without any mentorship from anybody and I also believe that you don't even need one to be successful. A mentor can help you speed up thing's, outline some mistakes he/she must have encountered when they started their business till it became successful, and a mentor can also guide you that's if you've a good one who's genuine and is not after your money but your growth and development.
There's nothing wrong in having someone at your corner because it will help you to make things faster and easier but then most successful people who are still standing strong till date are people who just learnt from their own lives, like failures, feedback from customers, loosing their jobs or crash or business and they had to ask around to know from people why things happened the way they did, and these things can even teach you better to what any human can do. There are people who had mentors and still failed, so not every successful person had one and not having one doesn't stop you from being successful, these days and time people are even learning without anybody putting them through it.
I can say that the way you are looking at mentorship or someone having a mentor is what instigated your view on this matter. A mentor is a teacher whether professionally (business and work) or casually. Most times, a mentor is usually an elderly person, who's there for you formerly or not. And now that we have mobile device and these level of technology, an online class or group may not necessarily answer or be seen as mentorship, but all the mental and other support needed for business or works are easily available nowadays.
A mentor is a teacher and everyone needs to learn and even keeps learning.