Five adventures in five years? One out of every 14 adventures he has? Yes, that's ridiculous. Christmas isn't the only holiday on Earth, let alone the rest of the universe. Why doesn't he ever happen across trouble on Easter or Tet or El Dia de los Muertos or the Draconian Molting Festival? Why this relentless fixation on a Christian holiday, particularly given that the majority of people in England don't even consider themselves religious? (Okay, granted, Christmas today is a very secular practice, more about Santa Claus than Jesus, but still.)
The reason is because Christmas is still the biggest holiday in the country that produces the show and still resonates with the audience. Nobody in England, in any numbers that matter, gives a shit about El Dia de los Muertos or the Draconian Molting Festival. It's also no more ridiculous than the amount of aliens who try to invade this one single planet that hasn't been established to have anything that that many galactic civilizations would come in these kind of numbers to take.
See the climax of "The Eleventh Hour." "Is this planet protected?" The bad guys left because they scanned their records and saw what the Doctor would do to them if they kept up their invasion. See also the big Stonehenge speech at the other end of the season. "Just remember who's standing in your way!" None of them wanted to go first.
I'm talking about the multitudes of aliens who had already put their plans in motion, who's advanced scouts in some cases, were already in place when the other guys put their plan in motion. Given how many races have been invading this planet, covertly or overtly, they would have bumped into each other behind the scenes, on Earth or in space. What would've been happening behind the scenes would've been similar to what happend in Venture Brothers when the Monarch's henchmen and Baron Unterbite's henchmen both showed up at the Venture compound to assassinate Dr. Venture. "Hey, we were here first!" "No, we were!" and then start fighting each other.
As far the aliens being to scared "to go first"......yet they have no problem invading the planet individually and going up against the Doctor, but when in the company of multiple war fleets all with the same goal apparently they shit themselves at the prospect of "going first". And apparently these conqueror races don't understand that no one goes first, they all attack at the same time. Riiiiiiiiight. That's infinitely more ridiculous than five or so Christmas themed adventures.
If all these races are that scared of the Doctor, then apparently all he has to do is just redo his whole "The Earth....is.....protected!" speech, set up some transmitters around the Earth and problem solved.
Look, it was a cool speech, but they totally undercut those races the audience is supposed to find fearsome.