Its gatwick, 3 lines go here, one every 15 minutes. I have always taken the train to either Heathrow or Gatwick, there's always been more than enough space to accomodate luggage, idk what people here are on about.
I mean, it probably depends on the train line? Only airport train I’ve ever had issues with was Manchester, and more due to an absolutely ridiculous ticketing situation than anything else.