But Google isn't a gatekeeper. You can go to hotels.com or booking.com or kayak.com or any site you choose as easily as you go to Google search or Google Maps. In what way does Google stop consumers from using competitive services?
Is simply having a more popular brand inherently anti-competitive?
No, having a very popular brand (>80% of market say), and then using that brand to kill competitors in another market is anti-competitive.
Google are not a gate-keeper for consumers, but they are for many kinds of business who want to be found on the net - they have no option but to try to reach the top of google in their domain, or in the case of this sort of move, actually pay for a presence in google results (because probably 90% of users don't look below this widget taking up most of their page).
If google uses their dominant search position to make sure that only google place links are ever seen and clicked, others might have trouble providing any service at all which does not go through google. There are obvious problems with that, and we even see problems today with companies who are penalised by google and cannot reach customers.
There is a tension here because some of Google's moves are actually good for consumers (say displaying maps), and not many people like using things like booking.com anyway (who are as you point out just more middlemen), but I think there is a legal case against monopolistic behaviour, and Google is getting very close to the kind of behaviour which has been punished in the past.
The bit I find interesting here is that countries no longer really have enough power to fully control corporations which are becoming truly supranational - this century we might find corporations become more powerful than even the most powerful countries. That puts us in an interesting position if say Google decides to take over a market or exclude certain users for monetary gain - who is going to stop them?