Exactly. What matters is not the total supply of the coin, but rather its use cases in the mainstream world. There are many coins and tokens out there with a deflationary model, only to experience a decline in demand because of their lack of real world usage. Bitcoin is the only exception, as it's not only a deflationary cryptocurrency, but also useful for people in the mainstream world. It's the one of the most actively developed cryptocurrencies in the Blockchain space right now. If you want to invest into good deflationary tokens, you need to look for those that are active in development and innovation with real usability. Otherwise, you'd be wasting your time.
Remember, one doesn't necessarily need to "hunt" for deflationary tokens if others with a undefined supply are doing well on the market. Consider Ethereum which is an inflationary cryptocurrency that has been quite successful over the years. It went from being worth pennies to hundreds of dollars (USD) in just a few years since inception. If you choose your coins or tokens right, your investment could be worth a ton of money in the future. It's all a matter of choosing the right coins or tokens with constant development and real use cases for the mainstream world. Just my opinion