Another comparison, since some like to bring it up, is the fall from movie to movie within the OG and prequel trilogies. The comparison isn't exactly a positive one for TLJ. I'll be using TLJ's estimated finals.
OG Trilogy
ANH - DBO: $307.3M/FBO: $314.4M/WW: $621.7M
ESB - DBO: $209.4M (-31.9%)/FBO: $247.9M (-21.2%)/WW: $457.3M (-26.4%)
ROTJ - DBO: $252.6M (+20.6%)/FBO: $165.8M (-33.1%)/WW: 418.4M (-8.5%)
Prequel Trilogy
TPM - DBO: $431.1M/FBO: $552.5M/WW: $983.6M
AOTC - DBO: $302.2M (-29.9%)/FBO: $338.7M (-38.7%)/WW: $640.9M (-34.8%)
ROTS - DBO: $380.3M (+25.8%)/FBO: $468.5M (+38.3%)/WW: $848.8M (+32.4%)
Disney Trilogy (So Far)
TFA - DBO: $936.7M/FBO: $1.13B/WW: $2.07B
TLJ - DBO: $621.1M (-33.7%)/FBO: $711.8M (-37%)/WW: $1.33B (-35.7%)
As you can see, TLJ will see the largest DBO and WW drops in series history, and is only outdone in FBO drop by AOTC. Speaking of AOTC, it saw the 2nd worst WW drop in the series, which at the time was seen as a poor performance. Of course, given that, at the time, it was the worst received in the series, it makes sense that it would have dropped so low.
As for Ep 9, I highly doubt that after TLJ it will see a 30%+ gain over TLJ that ROTS saw over AOTC WW. The reason ROTS recovered so much is because it was not only a better film than the previous two (even if only slightly better) and was the lead up to the beloved ANH, but it also showed the creation of Darth Vader, one of most, if not the most, iconic villains in cinematic history. Personally, unless it is an incredible movie (not holding my breath for that) I see it dropping more than ROTJ did. Probably, ~10%-15%. This would put it at $1.13B-$1.2B, or only 6.6%-13.2% above RO, a spinoff. Of course, it may drop even lower than that if it is a poor film.
