Charles said Cardano is aimed to develop the safest language to write smart contracts that would be not capable of any fault and meet the requirements for securities. Maybe that's why the development is a little long "in the tube". BTW, they released the book on Plutus to teach how to code in that language.
As long as development carries on in a safe and secure manner, there should be nothing to worry about. It's important to deliver a smart contract platform which is resilient against well-known flaws within the crypto space. As it's said in the real world, slow and steady wins the race. Cardano's development may be slow, but at least it has delivered as promised in its roadmap. Someday, it might be able to be in par with Ethereum as it adopts a VM and programming language of its own. Once it gets enough traction from developers, businesses, and individuals alike, prices will skyrocket for sure.
Even so, Cardano won't be able to overcome or destroy Ethereum in the future in the same way as altcoins cannot take Bitcoin's place within the market. It's best for crypto projects to work together, instead of trying to compete against each other in order to make the Blockchain industry a better place.
Glad to know that the Cardano team released a book with the aim to teach developers how to code within the platform's native programming language. This helps a lot in the mainstream adoption of Cardano, making it easier to develop decentralized applications for it. Considering that Cardano has achieved a lot since its inception, I'd say that it's going on the right track.
...that brings us to the history of Ethereum which in the past produced nothing but speculations
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True. I remember when Ethereum was called "vaporware", but all of that change once the platform was released by its developers. At first, Ethereum was extremely buggy but as time passed by, it became better and better. The same thing could happen with Cardano, as it grows slowly into a solid smart contracts platform for the masses. While it's still being developed, it wouldn't hurt investing some money into it for the long term. It could very well reach new ATHs in price once it gets a proper framework for the development and interaction of dApps.