There has been an influx of 600.000.000 fresh $ to the crypto market within the past days.

The entry door is very likely through Bitcoin. Given the current trading volumes, it is not crazy to suspect that up to 50% of this money is supposed to be traded into Monero.
Therefore we'll see a market cap. decline of Bitcoin somewhere around the $300 million range. This money will go into Monero within the next days. Let's just assume that a lot of profit taking will be going on.
Everything you said made sense except the decline in btc market cap. Surely the influx of fiat into btc is raising btc's market clearing price and hence market cap.
Fiat flows into btc. BTCUSD goes up. Btc flows into XMR. XMRBTC goes up. End of story until new flows occur. Btc wins, and monero wins². Only fiat loses.