I have heard this before, we went one year in the last week of July first week August and the hotel was empty no fights for sunbeds etc it was fantastic.
I have been reading that Spain has a very high volume of tourists booking this year due to people not wanting to take the chance going to Muslim countries, Tunisia. Turkey, Egypt Sharm etc so maybe this is right.
I have just put a search on Thompsons for holidays in Majorca the factory fortnight and their is page after page of holidays coming up
Thomas Cook has 7 pages full of Majorca holidays
Skyscanner reveals lots of flights with different airlines for Majorca so their are seats on planes available.
All the above are from Newcastle which is normally full up