I have used IG more often than the main entrance because I generally stay at Swan/Dolphin.
We have had a mixed experience competing with the main entrance to get to Soarin and TT. Sometimes we have been led all the way up near the rides and held at a rope with the main entrance folks also having a rope on the other side of the walkway. Sometimes it seems more like a free-for-all with no rope. The last two trips we have tried to get to TT at rope drop and by the time we arrived the line was already like 30 minutes long.
I understand Epcot sometimes “opens” a few minutes before 9AM and sometimes does not. So maybe we came a little too late to TT on a day it effectively opened earlier than 9AM. I think we got to the IG gates at about 8:40AM.
I am not trying to say anything negative about the IG. I would still use and do the same. Just do not get your hopes too high you will be on a level playing field with the main entrance folks. You may or may not. Thankfully with FP+ it does not matter as much as it used to.