World eaters sure got simplified but I wouldn't say IG did. Its about par for course, there's a mountain of subfactions although its much more designed as the "Choose your own" as opposed to "named" subfactions. On the other side, the world eaters essentially got straight up none.
Interestingly enough, both 8 and 9th were also declared as simplification of 40k, and to a large degree they were. They got rid of tons of the vehicle rules (Like facing, armor on sides/rear/ etc) and also streamlined huge phases of the game. It actually really did speed everything up.
What DIDN'T help, and is clearly what they want to fix now, is the bloat that happened in army books as opposed to core rules. The strategems are a really cool feature, but the sheer number of them exploded beyond belief. The subfactions were similar. The first few books had a few cool ones, but then it kept going and going. Pretty normal gdubs blat.
That said, I'm deeply unhappy to see a new edition. Its been about 'time', and its more or less on the schedule it usually is. But I'm just so tired of having to relearn a rule set again every 3 years, and especially when they've JUST managed to put out all the books for the last set. Its not surprising, again, pretty classic gdubs, but does mean I'll probably be sitting out most of 10th at the local store.