I've flown with a DH bike a several times and never had a problem. I always pack armour and spare tyres in the bike bag too, despite most airlines saying that the bag must contain only a bike. If challenged, I'd say it was essential packing to reduce damage.
Another issue we ran into a couple of years back was the interpretation of the EasyJet rules, even contradicting their own website and two different people at check in having different takes too.
Sometimes they allow a 20kg piece of hand luggage PLUS 32kg of pre-booked bike.
Other staff will argue that you get a 32kg TOTAL that includes both bike and bag.
The guys that packed all their gear in a bike bag/box got stung, I was fine travelling with one bag at 20kg and a seperate bike bag under 30kg.
It's all in the small print, the booking conditions, the prevailing wind and what time the check in person got up in the morning.
Of course, there is a potential that you could have 'forgot' to pack your bike bag with tyres/tools/pedals/armour when at the counter (where it's weighed) and have to re-distribute some items (how did they get behind that pillar?) before handing it over at oversize baggage (where it is scanned but has already been weighed!).