I don't know why you're being downvoted; this is a serious concern other vendors bring up when discussing windows defender (or whatever the free solution is called). At first blush the situation is very similar to I.E. shoving out other competing browsers.

People with actual knowledge in security, and observing the absurd designs and subsequent holes in 3rd party AV products, are secretly wishing MS do that :p

Speaking of...

I started my Surface 4 running Windows 10 up last night. The batter applet in the task tray reported, once I started up Chrome:

____________________

"Chrome is is draining your battery faster

Switch to Microsoft Edge for up to %%% more browsing time"

____________________

(Evidently, this was first reported in July 2016 http://www.nextpowerup.com/news/29282/windows-10-warns-about... )

There's no OS feature you can't say this about.

While I agree, that's the absurdity of arbitrary monopoly law, especially in the EU. (IANAL.)

Ah, but that's only a concern if microsoft has serious marketshare in the market of antivirus. Do they?

If people follow the advice of security practitioners, Microsoft will end up with the majority of the market, yes.