How are standing on this subject?

Are the xp nerfs that hard, or is a single lvl60 mage boosting alts a good strategy?

I know the issue with the character slot of the lvl 60 Denies other alts on that account. But one can correct that if the strategy it to lvl up multiple teams.

the basic point is what is faster? Grind the 5-man team to 60, or single lvl a booster (mage for exempel) boost the team and then correct the remaining slot taken by the booster, or perhaps the mage is part of the team.