Also tbh I& actually much prefer the Flash version of the very first note in S1 than the Legacy one. Like, let's compare:
There are two major differences between the notes - first is the obvious recontextualization of the event as a whole, but the second is tone.
In the original series, you were introduced to the world of Submachine slowly, starting out with things that could ostensibly happen in the real world and gradually adding more and more mysterious and supernatural elements. This level of familiarity helped new people get easily invested, immersed, and established great pacing for the mystery, letting the player spiral into the worldbuilding much like the researchers themselves.
When reading the new note, you are immediately introduced to a lot of new concepts at once: your questions are "what is karma", "what is the Structure", "what's the religious significance of Kent", etc. In comparison, the original note left us with just one question: "Can we trust this guy or is that third arm stuff made up?" - And you have to admit, that's a much more thematically fitting question considering Murtaugh's narrative.
As for the tone, the first game establishes Murtaugh as a bit eccentric, dismissive of his own safety (lost his own arm and didn't care? Kind of badass) and of others (looking down upon them), which explains a lot of his later actions. Of course he'd be careless with human lives, he views everyone besides Liz as below him because they can't understand him.
It has been mentioned before that the later games in the series feel like they're trying to retcon some of Murtaugh's personality traits, such as S9 recontextualizing his invasion of the Core in S6 as not motivated by revenge (although it doesn't really clarify what else he was seeking then. Just a chat with Liz??). However, because it's all happening in the later games, it feels much more like progression, following Murtaugh's journey of regret and redemption. It feels cathartic and satisfying. But making him softer and kinder from the very start, right in chapter 1? That undermines the catharsis somewhat.
Lore-wise, there isn't much that the new note clarifies or introduces either, frankly. In the later games, we already found out about:
The nature of the Kent waterfall as the source of karmic energy due to the crystal
The fact that Murtaugh lived in a highly structured and religious society (having his research team call him a holy usher)
The fact that the main reason behind the ostracization was from the actual deaths he was causing and not just because he was considered a freak
The fact that the society he lived in had access to karmic technology (they buried him using karma portals of their own)
And so on and so forth. The note rewrite ends up being a bit reductive as well, doesn't it?
So yeah. I& miss Murtaugh going "...but what the hell."