In as much as this is true, but a question still remains, is it better to hold or invest in something which is stable or that which appreciate in value? I believe most people if not all will go the one that appreciates in value.  This is just the difference between stablecoins and other coins. Just imagine Bitcoin is showing signs of uptrend, many who are in stablecoins won't hesitate to convert to BTC after which they can still move back to USDT etc, if they want. Therefore in my own opinion, stablecoins are just doing that which they are created for and with its restricted growth reduces its chance of being the future of cryptocurrencies. On the other hand, coin like Bitcoin is highly seen as the future of cryptocurrencies because of its value and potentials.