Seems particularly unfortunate that despite being able 380 you ended up much lower, gives an idea of how busy things were. The problem in that part of the world is that Shanwick has to come to a 'gentleman's agreement' with Santa Maria each day as to which levels are available for westbound traffic.
Generally, traffic running south west for Florida, the Caribbean, Mexico and all points south entering Shanwick via BEDRA, OMOKO, LASNO, ETIKI, SEPAL and SIVIR are allocated even levels. This enables traffic running due west for the east coast US/Canada entering Shanwick between ETIKI and SIVIR, coupled with similar traffic entering Santa Maria via HIDRA and MUDOS, to use odd levels. These two traffic flows cross between 20W and 30W, which during peak times creates problems in a procedural environment where huge Oceanic separations soon use up the airspace, particularly at optimum cruising levels.
Furthermore, OMOKO can be especially busy on certain days as the fixed route between the British Isles and Canary Islands, Tango 16, enters Shanwick at OMOKO. Therefore hotel change-over days for the 'bucket and spade brigade' will result in the levels available for Shanwick traffic via OMOKO being maxed-out PDQ.
As clearances are issued on a first-come first-served basis it can simply be pure luck in terms of timing whether you get a 'good' level, or otherwise. Making the Shanwick Planners aware of maximum levels able at point of entry, together with any flexibility in terms of speed or route may help get something more palatable. Rest assured that the Planners do their utmost to find the best clearances available, but sometimes there's just too much metal for too little air.
Better luck next trip.
