The reality as CS explained to you is that Airbnb prioritises hosts in the rankings with earlier availability.
As you are full until June it's unlikely that Airbnb will put your listing high up in its rankings. It's purpose is to convert as many guests as possible to bookings. Promoting listings that aren't available won't help them to achieve this.
As it gets closer to the dates you have open you will move higher up the rankings. Those looking for properties like yours later in the year will still see your listing when the search for later dates.
The majority of guests will put in dates when searching so this is not too much of a hinderance for you in terms of your listing being visible.
Remember don't just rely on one marketing channel @Daniel85 there are other platforms you can use along with direct bookings.