Sorry but that is such a bullshit narrative and one that I've heard a few people spouting and drives me utterly crazy.
The Europa is a lot harder to win than an FA Cup. For starters if you are in the Europa you have to play a minimum eight extra games and all of the travel that entails, Thursday > Sundays which we know is an absolute killer. And probably contributed heavily to our injuries.
Then you play home and away another what 8-10 games home and away to actually win it?
You make it sound like away to Frankfurt in a hostile atmosphere is a piece of piss...
The FA cup, you come in at the 3rd round. Play what? 5 games, no replays, straight to penalties and its totally random. You might win it without having to play any of the teams you mentioned. Most times you might play one of the clubs you mentioned.
I love the FA cup but it is nowhere near as prestigious or difficult to win as a Europa. People say this because we played Bodo Glint in the semi's but I like to remind them that Bodo side knocked out Lazio, hardly a small club.