While I agree there are a very tiny number of boutique Travel Agency, some which might primarily concentrate on Oceania and Regent, that universe is small. As continually demonstrated on this Forum, many of we cruisers are not solely wed to Oceania. While my TA is a high volume Oceania seller, my of those cruisers likewise sail Azamara and Celebrity. Being a boutique, and not a member of a Consortium, may mean the Agency avoids Consortium fees, but it also means they miss out on the various Consortium deals for many lines that aren’t available to the otherwise small volume Agencies.
If one is a dedicated Oceania only cruiser, then the boutique will work very well. If not, a member of a prominent Consortium will work better. That is , of course, except for those that change Agents like they change their underwear.