I think any contention that people are returning to the game because of champions is definitely speculation - I haven't seen one case of that. Something like MOD EE is much more challenging than champions and most of the people with all the past lifes and gear on Sarlona don't want to run that.
I just question whether champions are doing what they are intended to do since they effectively only challenge low-PRR characters. I was leading an EE PUG Orchard run almost every day for about 2 months and I can tell you the average player isn't finding EE easy. I see alot of people die and I see people sitting at -500 or higher after getting hit from a champion.
The combination of armor up and champions broke the game for people with low PRR that don't have several divine/PDK past lifes. Fortification used to be an equalizer that prevented damage spikes for low PRR characters but there is a specific debuff that eliminates only that layer of protection. The PRR debuff in TOEE could have been done right to target PRR as a percentage, but it was done as a fixed # so again this debuff specifically hurts players with low PRR much more.
I don't really care what Turbine does with champions, but I think the system is very flawed and limits build diversity for people that want to run EE. For some people, having to TR to make a champion-friendly build is not something they want to do.
The only true measure Turbine has about whether champions are driving away casual players is revenue. If revenue is down there likely was an impact of champions as casual players tend to spend more $ per hour playing than hardcore players. Their loss isn't as apparant on total playtime #s since they tend to play less than the hardcore players.
If revenue is up or neutral then it's unlikely champions are driving away casual players.