There is an estimated 208 000 tonnes (208 000 000 kgs) of gold available on planet earth. This has been mined throughout history and we can assume that this is not lost. But let's estimate it at 210 000 tonnes to make it easy.
I believe that there is much more gold than those predictions, but even if the data you present are correct, what about the gold that has been talked about in recent years and is located outside the planet Earth? Of course, that gold is not available today, but the predictions are that in a maximum of 50 years it will be commercially available in quantities that will far exceed the reserves on our planet.
The amount of bitcoin that will ever be available, is capped at 21 million coins. So for each coin that is available, there is 10 kgs of gold available (210 million divided by 21 million = 10)
At the moment, no one is seriously talking about increasing the max supply, but it is still something that should not be completely rejected, because who is to say that some new
"visionaries" will not decide in 20 or 30 years to change the code a little and add a few million new Bitcoins. People are prone to stupid things, and I wouldn't be surprised if they add another one to their list of stupid things.
- Sales of gold are already subjected to taxation in nearly every country. I don't know if the government will succeed in taxing BTC. I guess only if BTC needs to get converted to currency, because then the banks and the IRS get involved. But if we can avoid that conversion for payment (directly in BTC), the IRS and the government are bypassed.
I don't need to pay any tax when I buy or sell investment gold, and I think this is a law that applies throughout the EU, although there are probably exceptions from country to country. And regarding the payment of capital gains tax when it comes to Bitcoin, in most regulated countries there are laws that clearly regulate this and the procedure is not significantly different from the payment of capital gains tax from other investments.
In addition, even the EU has several countries where capital gains tax is not paid if you sell Bitcoin 1 or 2 years after purchase.