Well no offense to the old greats, but have you ever gone back to read a Stan Lee comic?
Admittedly, I didn't grow up on him. But the guy can't write for beans.
The characters a brilliant, but the writing was always uninspired.
Obviously you don't know what it's like to write a story. You can ALWAYS find something to improve on.
Rather than Marvel telling these writers to start from scratch and erase everything 616 has established (as you imply.)
They simply said "Oh? You want to take your own spin on it... fine, here's an alternate reality, take your own test drive with these characters. Just leave 616 alone."
Marvel did comic fans a favor by creating the Ultimates so that we could get a fresh take WITHOUT erasing the past as well as keep the established story lines we've had for 40+ years.
And even the amazing comic book films out there took liberties, and I think they ALWAYS should. If I want the old stories, I'll read them. I have them. I want new and fresh while staying RESPECTFUL to the source material. By that I don't mean changing a look here or there, I mean changing themes.
Like in Ang's Hulk when Banner's character was loving the "release" of the Hulk, eck. Totally goes against the theme of the struggle.
Or like Ultimate Hulk, they kept the struggle, but screwed with the character far more than TIH is doing to Abomination. Making him a sex crazed maniac cannibal... THAT is when I hate the Ultimates... not when Peter Parker is battling a Hulk like Green Goblin with fire powers.
Though I'm not to fond of the Ultimate line of books, in some cases, the liberties they've taken aren't to far off from the characters 616 center. Then you have extreme cases such as the Hulk. Frankly, I think Marvel is running out of ideas for the Hulk.