You are wrong, the online business will almost always be valued at less than the offline business and for good reason. But more important is that your analysis is way too simplistic.
If you want to sell your business then there are many ways where you can sell it because there are many people who are interested in business.You can sell it at online which becomes very popular from last many years.
If it was a business which I made just to make money, I would sell it for reasonable price. But if it was my dream business, I would never sell that!
I didn't give an analysis at all so I can't be wrong nor can my analysis (which I never gave) be too simplistic. As for an online business always being valued at less than a physical business that is a statement that can't be made. But one thing is for sure if both businesses have the same overhead, assets, and profit margins one cannot be valued less than the other by the standards of an investment.
Why don't you explain then. If 2 businesses have the same overhead and profit margins, why would one be valued less than the other?