In terms of OW, some people want an IG experience true to the Codex-expressed IG: endless ranks of guardsman throwing away their lives in a giant horde, the hammer of the Imperium to the Astartes' sword.
Why would any want to play a faceless, nameless character whose only role is to die, forgotten and unmourned among hundreds of his fellows? This is an honest question. I do not comprehend the entertainment gained from that experience, especially given the time and effort required to make an rpg character.
The easiest way to satisfy both desires is to start PCs closer to the former, and if you want to make them like the former, simply give your PCs a few thousand extra XP at character creation, and maybe hand each of them an extra Fate Point (that they presumably would have earned while gaining the XP). Presto, instant Hero-class PC. But to demand that all PCs start at that level robs others of the chance to play the average guardsman.
But that isn't what I want. You will note I didn't name Guant in my list of characters to emulate. The guys are I named are, IMO, average if heroic Guardsmen. Sure Corbec and Rawne has senior officers, but only by right of being the only guys left after the fall of Tanith. If you read my second post, you'd see that is what I want - to play an average albeit heroic Guardsman. As it stands currently, PCs aren't even that. They start as below average guardsmen.
I'm not sure how many ways I can phrase this, but just because you can't comprehend it, doesn't mean it's not the case. Additionally, for many people creating a character doesn't take all that much time and effort (I can probably make a BC or RT character in 15-20 minutes at starting level, easy). You also assume most people play RPGs for the roleplaying aspect, whereas I know some people who enjoy it just as much for the gameplay (or crunch) or just as a collaborative group game rather than an acting experience. I can't tell you why people have fun the way they do, but trying to force your opinions of "fun" on them isn't the way to go. Again: people play RPGs differently and for different reasons.
As to your second point: how does giving more XP to your theoretically "below average guardsman" not solve your problem or give you what you want? And both Rawne and Corbex (Rawne especially after Gereon) are far, far away from being "average guardsmen" in any sense of the word.
And I did re-read your second post: I literally cannot understand why you're so intent on comparing PCs to static Guardsmen, or why if starting level guardsmen are too weak in your eyes you just can't start your campaigns with 2-3k extra XP. Please explain further, because I'm genuinely not getting it. PCs exist on a spectrum, depending on how much XP their GM started them with, how long they've been playing, etc. It's like pointing at a DH Ascension character and saying it's way too overpowered compared to the base enemies in the DH corebook. PCs by their very nature are extremely malleable in terms of their power, which is what sets them apart from static NPC profiles. And like I said in the last post, it's good to have the option of playing at either end of the spectrum, and not forcing players to start on the high end just because it happens to be one person's preference.