“Bitcoin is not backed by anything”

I was recently watching a finance podcast where the host responded to a question by someone pro Bitcoin. The host responded that “Bitcoin is all speculation and is not backed by anything”.

Having read the white paper Satoshi makes a mention of the value at least being that of the energy expenditure to mine bitcoin and secure the network.

I somewhat get the concept of proof of work and energy being tied to value but is there a better explanation to bitcoins value besides this and a good rebuttal to someone saying it’s purely speculation?

Another reason I ask this is I recently found out that between the year 2100-2200 there will only be one bitcoin left to mine, and so, 100 years is a lot of energy to pump into one bitcoin. So with this in mind it makes sense for the price to very closely be correlated to energy consumption cost - if energy becomes really cheap by then what does that do to the cost of a bitcoin?

Please correct me if any of my statements are incorrect or misleading.

Thanks!