It's true that the ROMs are a bit easier than real games?

No, I've played a ROM of and a legit copy of Leaf Green and I found both of them to be equally hard.

Depends if you play like I do:
-Use the VBA speed up feature to cut down time training.
-Create save states when catching rare pokemon to waste less pokeballs

Otherwise its just as hard as the actual games

Not realy, it deppeneds honestly how you play.
my freind has one of these and has cheats everywhere on there and has tons of Legendarys. if you play that way it is easier.

But if you just play normaly then its the same