Although my oldest skipped 6, I would say that for most kids doing 6 then skipping 7 makes more sense (or doing both). Level 7 with bonuses really could be level 8, and level 6 with bonuses teaches a kid almost everything level 7 does - IF the kid is a strong tumbler and on vault....full bonus L6 has many of the support event skills needed for 7/progression to 8, but L6 floor and vault are very easy compared to L8 options....and my son spent most of this year focusing on progression, not routines - so he's really ready to build many of his L8 routines already - doing L7 this year was a "building year" - he did well overall but didn't spend time perfecting a twisting yami, for instance, but worked on his Tsuk and his FHS-FT vaults....
My older boy really just needed to "get a move on" things - and hasn't gotten full bonuses at L7, but in retrospect L6 would have been super easy and boring for him....plus he's "old" - at 14, and a late starter, but has good form in everything he does and his weaker events (pommel primarily, but also Pbars and some rings skills in past) have come a huge way this year with strength and additional training - and at L8 he'll be fine....he actually placed in pommel at states! (small group, but still)....
Our team has far more kids repeat than skip - and some even do 3 years a level - taking the time to get form and strength at some point is key - my younger boy is really starting to put those together (finally) - and a second year of L6 will do him wonders if he continues to like gym and work hard...