It's like saying Boeing has a monopoly on airplanes, when actually they can be said to have a local monopoly within a few hundred km of Seattle.
It's inconceivable that any forum dominantly by Apple, Microsoft, Alphabet/Google, Amazon, Meta/Facebook, Eli Lilly, Visa, Novo Nordisk, Walmart, ExxonMobil, JP Morgan Chase, Johnson and Johnson, LVMH Moët Hennessy Louis Vuitton and Saudi Basic Industries (SABIC) is ever going to propose anything to threaten that power.
You've already shown to be not entirely genuine in writing comments, so this seems like digging a hole. I'll give you another chance to come clean and engage productively, will you do so?
Just go away.
This might make sense if I was the one who wanted to engage first.. but it's just nonsensical in reality.
The problem is that if that dominant player does something (like raise prices), you cannot escape them. The rest of the market does not have the ability to absorb all the people who would like to flee the dominant player.
The problem is Always Late(tm) inventory combined with process optimization. No competitor has significant inventory or excess capacity, so nobody can respond to sudden consumer changes. Covid toilet paper shortages were a great example: industrial toilet paper suppliers were unable to deal with the shift to consumer and consumer toilet paper suppliers were unable to deal with the demand shock.
What the number should be is up to some interpretation, but I suspect that no market should ever allow a player with more than 25% market share no matter how you define "market".
IIRC Google controls about 90% of the online ad market out side the walled gardens like Facebook.