Here I start, with the mining process and its excessive use of electricity, there are coins like NANO that have zero transaction fees, and can not be mined and no harming the environment.
How important is mining to be one of the downsides of Bitcoin (the largest currency) so far? Why was not resorting to an easier solution, as in these currencies today?
The example you gave, Nano , is a centralized cruptocurrency. What makes bitcoin special and value is its decentralized nature.
There is no central authority confirming transactions or deciding what the network will do.
Mining is what makes bitcoin decentralized. Anyone can just buy some hardware and start mining. The electricity spent in mining isn't wasted , it is used to secure the network.
If you just want fast transactions, you can just go on Visa. Bitcoin has a different goal, which is to let people control their money, without any CEO or president or central bank behind it. The code is the law.
PoS coin are still very incipient, and even ethereum is struggling to try to make it work. Bjtcoin is more conservative, and there is no room for errors.
Why with so many options (replace by fee and the like), would it have been so much easier to just send and receive bitcoin and at the same time be decentralized and no mining?
There is no other coin as decentralized as bitcoin.
Many of those coins just change Block size or block time. They are just changing parameters, not creating anything really new.
