Nothing wrong with this question. A few years ago new hires were getting 767 right out of training. That stopped because the fleet is shrinking. 75 & 76 are same bid status and pay less. So since the 78 will likely replace 76 it may become more and more junior. Also saying there are 140 out of 1000 airplanes.. do the math is not helpful and how does a person who doesn't know about these things do that math? There are a lot more Group IV FOs than Captains. PHL(A330)Miami and NY(777) are most junior at around 11700 of 15,000 ish pilot. It seems to get more and more junior so hard to tell where it will be in 5 years. Especially if they end up getting more 787s.Lowest 767 about 14300 which will get you some Europe out of NY.
It's a lot harder to predict these things at a big multi fleet airline. Sometimes there's no/little movement on some fleets for long periods then a big surge forward.