Christ, the 'second to Disney' claim is the most skewed debate used by enthusiasts. Merlin claim (quite rightly) that in terms of attendance, they welcome more guests than any other operator - that is true. If I am wrong and they have claimed that they are producing rides or experiences in the same league as Disney, point me to it - because I've missed it.
From their official
Merlin Magic Making minisite:
"(Our) primary aim is to raise the bar in terms of innovation and creativity, allowing Merlin to stay ahead of the competition. No other company on the planet delivers projects of such quality, with such value, within the timescales achieved...
We .. produce unrivalled, amazing content for our attractions, build at a speed and value unknown to our competitors..."
By competitors and "no other company on the planet" they obviously suggest Disney. Also internally, to all staff, they mention and compare themselves to Disney very frequently. They very regularly claim their mission statement is to became the global leader in "location based entertainment" and to "beat Disney".
They measure their attendance so that they can make the claim, because whichever way you measure it, they know the connotations of "Second to Disney", don't pretend it doesn't imply quality and general brand gravitas that Merlin havn't actually earnt with their output. They want to be "First" in the world at all costs, in whatever measureable way they can get to first.
Of course we know that their Disney comparisons are a load of rubbish when most their park operations are run so amateurly, the scenic and effects maintenance is done DIY across most parks now, new attractions are always plagued with problems and rely on hefty gimmicks, etc. But then again, Disney seems to be going the corporate route too recently, despite their work being of infinitely better quality.