Buying altcoins is not diversification. When bitcoin goes up, altcoins go up. When bitcoin goes down, altcoins go down much more. You are not negating risk at all by buying altcoins, which is the whole point of diversification. If you get really lucky and catch some random pump and dump you might make a little profit, but the vast majority of people who hold altcoins lose money. Just ask anyone who bought pretty much any altcoin during the bullrun at the end of 2017. 99% losses from their ATH is commonplace.

If you want to diversify your investments, look at vehicles outside of crypto altogether.

If a project has stopped being developed or worked on because the price has fallen, that's a pretty sure-fire guarantee that it's a trash project and the creators/developers are only in it for the money. Look at bitcoin in comparison. New releases and new features being worked on constantly, regardless of whether the price is $3k or $20k.

That's a problem with centralized exchanges, not with bitcoin. I trade peer-to-peer, and for the vast majority of my trades I pay fees of around 1-3 sats/byte. If you are paying 0.005 BTC per withdrawal, or whatever these scummy exchanges charge, then you should be looking for a new method to buy and sell bitcoin.

The reason altcoins confirm quickly is because a confirmation on an altcoin is only a fraction as secure as a confirmation on bitcoin. A litecoin transaction, for example, takes more than 36 hours to reach the same amount of security as 6 bitcoin confirmations.