Well you're looking in Lexicanum, the unofficial Wikipedia for Warhammer 40k. But with all of this let's put it at the end of the Age of Strife, and the Empire I'm referring to is the Fel Empire. But if you don't like it, feel free to ask me to change it.
I think I give up. This is getting hard, because the Time point keeps changing. It makes my arguments almost meaningless and to me it's like trying to hold a gallon of water with only your cupped hands.
You want my analysis of the strength of Humanity in 40K?
Pre age of Strife: Humanity would royally kick the ever loving s*** out of anything in the Star Wars galaxy, from the ancient armies of Jedi to a fully mobilized Galactic Empire to even the Fel Empire or Darth Krayt's Galactic Empire after it. At this point in time humanity had means of mass producing every technology seen within the IOM in the 41st millennium and then some, from Powerful AIs and Legions of Automated Soldiers to stuff that we've never even seen before. The only things they didn't have were Space Marines, and Titans, but they had the support of every human planet populated in the galaxy, and maybe even some alien allies.
Age of Strife: if it weren't for the vast instability of the space in the Galaxy due to Warp Storms, it would be a cake walk for even the Rebel Alliance (Not the NR). Since these storms lasted for quite a while (millenia IIRC) and were ever shifting it would make any attempt by any Star Wars government at attacking futile. But there would also be no resistance anyway since most Human worlds went Mad Max. The only real defenses would be on Terra and whatever planets the Adeptus Machanicus were able to get to through the Warp Storms, as Terra had the Emperor and his Proto-Space Marines and the AMs had their Titans that they developed at this time.
Post Age of Strife: Aside from the actual Age of Strife this is the Weakest the IOM would ever be. The Emperor would have control of only a handful of sectors, he would have very minimal resources, and his armies would be his first generation Space Marines (Not as good as later Generations like the First Foundings) and the presumably millions of warrior bands that swore allegiance to him. He wouldn't have his sons as after he created them they were teleported away
by the Chaos Gods that viewed them and their father as threats, and the newer Space Marine Legions suffered from not having their Primarchs, as well as the fact that lot's of Tech was still missing in lost STCs scattered across the galaxy. So if it were at this time against any Star Wars government then it would be like kicking a small child.
The Great Crusade: That small child that you wanted to kick has come of age and can kick back. The Vast legions of Space Marines are at their peak strength. The Armies of Man have the weapons and ships they need. A large percentage of the Galaxy now belongs to the Imperium of Man, lead by the God Emperor of Mankind. Lost technologies have been discovered and are still being discovered, as well as new technologies being developed for the first time since the Age of Strife began such as the Webway
gate the Emperor was building under his palace on Terra.
Post Horus Heresy: Utter Confusion reigned in the IOM, their leader nearly dead and completely unable to govern. More than Half the Armies turned traitor wiping out more than half the forces that Stayed loyal. Not a good time and it wouldn't be again for several millenia.
Pre Modern: Finally the IOM begins to regain the power it once held when the Emperor walked among Humanity. Though the times have gotten harder since. The Legions of Chaos mount ever more powerful raids and Crusades into IOM space. Species that were once too young to bother the IOM have developed (Tau). Once populated worlds are raised by an unknown enemy that has technology far in advance of anything Humanity has ever seen (Necrons). A Plague of Ravenous Death descends on the galaxy eating everything in it's path, and leaving dried and dessicated worlds in its wake (Tyranids). And sensing all the battle that the other races have stirred up the Orks spread in ever increasing numbers, readying for the Whaaaaag! to end all Whaaaag!s. At this point the Galaxy is on the precipice of annihilation.
Modern: There is only war. The IOM is besieged on all sides by all the threats of the Galaxy, what power they did regain is slowly slipping away under this onslaught. It's hinted at that everything comes to a head in the later days of the 41st millennium, though if that happened GW would be out of a Game. So, stories tend to blank out here, and only try and remember the "good times".
Pick one and stick with it, please. Then I might Re-consider leaving this debate.