We have enough EL experience in the past few seasons to see through this myth, if we choose to ignore the evidence from other clubs.
We didn't really give our youth a proper chance. Our starters still ended up playing a lot especially in later round. Doesn't improve our level when we're back into CL.
Teams with 'eritage' in EL like Sevilla is not powerhouse in CL despite the excuse from Mourinho. The like of De Ligt, F.de Jong did well in CL because of their quality and experience being the starter in all competition. Not because the exclusive experience in EL.
What the point of young players who unlikely to make it as first team player, let alone starter to gain EL experience, when there is a trade off with playing Thursday and Sunday/Monday? Trim the squad, sending young players on loan would do more good than a handful of EL games where the managers don't know his young players and his opposition well enough.
When you're in EL, you will have to have desire and the mean to go all the way, or it's pointless having your schedule shuffled. With the creation of ECL, getting out has become more difficult because you have to endure the embrassment of finishing bottom of the group, to wash your hand off this competition mid season.
So it's better to not be in it from the beginning.