These are just 3 examples of thousands of acquisitions by big companies with dominance in their industry. The trend is very clear, a handful of companies buy out competition and own virtually every serious competitor in the market. There are ongoing lawsuits against tech companies for doing this, and unfortunately companies can lobby to keep the laws on their side. Also, businesses like BD are always going to tend to want to sell rather than compete, this is obvious.

I don't see how one could argue there is no natural tendency towards monopoly capital given these key facts.

This is a key point of Peter Thiel's in his talk at YC from some years ago. He expands on it to great effect in a few other videos too: https://www.youtube.com/watch?v=vtJ0C0UHFfE.