"Hero"
Hero is a subjective term and to say that characters will be "more heroic" is somewhat silly IMO.
In my mind, I always determined that a D&D character became a "hero" (1st level PC) the moment they decided to step out of a mundane life and decided to become an adventurer.
With that notion in mind, I find 1st level 3e characters appropriately "heroic" though there are certain circumstances where I find the system lacking. Mostly in relation to skills and general ability rather than combat statistics.
As just a way of making the system better, I wouldn't mind seeing 1st level characters have a few more hit points, but not quite double current first level hp.
For the "fighter knowing how to use 40 different weapons" statement. I think this is being addressed in 4e by fighters having more specialized maneuvers with their chosen weapons. I don't think it was necessarily designed as a concept with intended ramifications in a discussion questioning the heroicness of a 1st level fighter, but rather to simplify the weapon proficiency system.
As for the "why send 4 1st level characters instead of NPC guards to solve a situation?"
There are a great many ways to address this question, but it can also be asked even if the PCs are higher level. "Why not send 40 NPC guards instead of 4 3rd level PCs to solve the problem?"
Militia might be on short supply. The PCs might *be* the militia sent. 1st level militia usually don't train in sneaking, opening locks, finding traps, casting spells etc. etc. So they may have some talents or abilities that the guards don't.