One of the challenges is distinguishing the various brands - many of which would be considered competitors in most markets, and virtually inter-changeable in the eyes of the consumer.
This Skift opinion piece, Every One of Marriott's 30 Brands Explained is a very thorough rundown of the current Marriott and Starwood brand messages along with some commentary of perhaps where the brands will (or should) go to differentiate themselves and maintain share.
Something to keep in mind if it appears a Marriott "monopoly" will impinge competition is that the vast majority of hotels are not actually company-owned. Individual hotel owners and hotel owning companies will continue to demand their share of the business.
And then you have *us*. My job is to create competition for my clients' business - no matter who owns the bricks and mortar, or flies the flag on the top of the building - I will ensure hotels sharpen their pencils and offer the best possible prices and terms, regardless of who they're competing against.