The price fluctuates greatly, or there is no hedging, it is a bubble
The price is not regulated by any market mechanism, which isn't desirable if you're looking for a stable asset. It won't be, unless people decide to not panic over every little FUD, probably not going to happen. I predict Bitcoin to be far more stable in the future if it gains a more stable footing.
Has not been accepted yet, you cannot pay in most shops
Save for businesses located within restricted regions, loads of online shops have adopted it. It provides intrinsic benefits that various payment processors cannot provide. You can absolutely accept Bitcoin in your brick-and-mortar store as well, that is closely tied with the local adoption rates though.
It faces a serious defect that the government/people are unwilling to give up the right to print money, so they will stop it in some way.
That is why Bitcoin exists.
Thousands of coins = inflation. I don’t think this is true, because every POW system with a smaller computing power, Bitcoin can theoretically be "cracked" by the computing power provided by btc miners, plus the computing power can be comparable to any other computing power in the world. Comparable. Compare with the network or supercomputer, do it yourself. )
Bitcoin is not secured purely by POW, it is the game theory behind POW that secures it. It is described in the whitepaper.
You cannot compare ASICs with supercomputers. ASICs are incredibly optimized and designed for one specific function, which is to hash the blockheader again and again until it finds a suitable hash. Using a supercomputer for that function does not scale, it is far more efficient to design and build something for your specific function.