If you try to gain knowledge in various platforms, you will know all the new features and how to use them. You will also be able to shift from one platform to another depending on your needs. You will not be tied down to a particular platform, making you adaptable to the situation. But it is better to specialize in Ethereum because it is the most popular platform for developing decentralized applications. And observing the market trend, the usage and popularity of Ethereum are rising, and specializing in it will enable you to decrease working time and increase efficiency.