Stock market's moneys can flow to and from gold, and it just did now in corona pandemia. and the same could happen to bitcoin as well. [...] When the price of a stock falls the company do not get under-financed.
This is all true, but it occurs on relatively small scale. In the Corona crisis the gold price increased 20-30%, it didn't multiplicate, which would be necessary if a large part of the stock market investments went into it.
My point is that it's not like the image suggests: that the market cap of Bitcoin could become so big that a significant "share" of the money which is put today in the stock market could flow into it and stay there sustainably.
Stock price is just a speculation about the future of the company, mostly based in companies' capacity to pay dividends.
Exactly. But let's examine the crisis example in detail: if a relatively large part of the money of the stock market would flow into Bitcoin and gold, then the relation stock rentability/dividends eventually would become distorted. After a time, if the companies at the stock market continue to be sustainable and recover from the crisis, it would become attractive again for the money to return to the stock market to be able to profit from dividends.
All what would be possible from these movements was a short price spike for Bitcoin, and on a relatively small scale. I think it would be similar to the spikes the Gold price sees in crisis periods, not more than that. So the amount of gold and currencies together continues to be a better number to be compared to the "potential market cap of Bitcoin".