Is it just a trading commodity, long term investment or is it (very very very) slowly replacing fiat. I know there are many companies and small shops that accept cryptocurrency but is that it? Is the problem still about the speed of a transaction
Please help me catch up a little

Combined all of them, the problem is not only about the speed of transaction, there are other problems too. In my opinion bitcoin still same like the old time, the different is more people start knowing about bitcoin and learn about it, also find an opportunity in bitcoin too.