Most of the people complaining about massive depreciation overpaid when buying new.
Most of the people selling at a high price overpaid when buying new and have their heads in the clouds about what their RV is worth. Basically, they expect you to absorb their poor research and ability to negotiate.
I've bought my last 2 RVs brand new and will buy my 3rd the same way.
In my experience TTs and 5th wheels are worth roughly 50% of their MSRP around 3-4 years from when they were purchased. If you paid 90% of MSRP I can understand your frustration. If you paid 60-65% like me you're very content with the cost of ownership and benefit of owning a new unit with a warranty that doesn't smell like some else's wet dog and dirty feet.
To each their own.