I've never called myself a "hardgainer". It's true that most people are not willing to put in the effort required to eat a lot. For me it was always the hardest part. For others, it's easier. But it's also true that genetics play a big part in how fast and easy you gain weight.
Anecdote time:
When I was younger, 20yo, I did a 3 month contest prep for a bodybuilding show. I ate exactly the same every day for 3 months, about 5500 kcal* - and lost weight. I didn't use PED. I'm 6'1" and went from a very lean 190lbs to an absolutely shredded 176 (79.9kg = under 80kg class). My point is,
I lost weight at 5500kcal. I "trained" (exercised) 4 or 5 times per week and did 1h LSD cardio/day. Bigger guys than me always marvelled at my ability to put away food. I only started to gain weight beyond 190lbs when I dropped my ridiculous training volume. I knew a guy who weighed 30kg pure muscle more than me and used 2800kcal for his contest diet.
*
- 875g of white rice = 3010 kcal.
- 2.2kg of poultry = 2300 kcal (? there are a lot of different numbers to be found online, this is using a lower kcal one).
- sometimes replace 400g poultry with 400g fish in one meal.
- teaspoon of Olive oil (50 kcal) and an apple (80 kcal) a day
I'd do it different nowadays... but it worked :P