Timeshares are risky investments (if they are investments at all). A fair economic rate of return on the capital used to purchase a timeshare is in the 15-20% and perhaps more -- given the lack of control, illiquidity, risks, and use restrictions. Comparing a bank rate of return (where the principal is guaranteed by the federal government and is totally liquid) to a timeshare rate of return is like comparing apples to (rotten) oranges.
Any competent real estate or business appraiser using a typical buildup rate (Ibbotson, etc.) will come to this conclusion. Think about it: you can buy a relatively safe real property investment and get an ROI of 5-10% -- and that's for an asset such as a single family residence to rent, a shopping center or an apartment building that the owner controls, can borrow against, and that may even go up in value.
In contrast, timeshares are subject to rapid depreciation, sometimes intentional. When Marriott raises the "education fee" on points resales, point values decline. When DRI takes over a project, values decline. When a shiny new project goes in next door, values decline. When MF's go up, values decline. And as owners, we have zero control over any of this, except to sell at the diminished price. (None of this even considers a developer purchase which is a 99%+ guarantee of losing money.) One may hope to resell a resale purchase for the same price years later, but that is the exception, not the rule. Most timeshares lost 50-99% of their value between 2008-2011 and never recovered.