"Keep the bad takes coming people."
If you're going to be like that, I can play this game better than you.
More jarring, more like. The presence of fantastical elements before the Eclipse makes it more believable. That's why they're there. Switching from pure realism to the horror of the Eclipse without any of the fantastical seeds may have been more "impactful", but not in a good way.
Do you really need to see even more monsters than the ones that are shown to know that they are coming? The seeds are there, I don't need more than one character saying to Guts that he's doomed to get the hint. In manga release time, it makes sense, more reminders here and there, in anime, it gets repetitive.
Black Swordsman's importance to the story can't be understated though. It establishes what kind of story we're going to be told. Other than that, the presence of characters such as Puck so early on not only plants the seeds for further layers of this world (i.e. it's not only horror and demons), but also adds much needed humor and levity (which also tells us what kind of story this is. In other words, not just darkness and folks getting raped).
Within the specific arc the anime is adapting, Puck is superfluous.
Wyald's purpose is not just to show Guts' progression as a warrior, but to demonstrate his capability to handle such monsters at that point in the story. It makes his survival of the Eclipse more believable.
People always use this argument and underestimate the suspension of disbelief most people are willing to give when seeing the main character fighting monsters. Or are we in that state of fandom where we talk about power creep and power levels and how Guts would not have killed that many apostles without a sword at that point in the story, etc, etc. We don't need Wyald to remind that Guts can survive in extreme situations. It's filler and it's gross and greatly lessens the impact of the Eclipse.
Casca's role is important too. If anything, this part enhances the Eclipse, as it serves as a contrast between the two situations (as in, nothing they do during the Eclipse could have gotten them out of the situation, as opposed to the Wyald fight).
What? Casca's role is important how? Rape fodder for the nth time? Enhances the eclipse? It lessens it because it desensitizes the reader. But maybe it's like Lucas said "it's like poetry, it rhymes", in this case she only almost gets raped, one volume later she's raped twice, it's such an important plot difference, that Miura should keep this motif in every arc (he kinda does).
The stuff with the "rapes" needed to be shown to be impactful, I'd say. Especially Guts traumatic past. They hinted at this in the 2012 films, and that had no impact at all. It was just awkward.
Guts has a severe reaction to being touched, do you need it to be spelled out?
As for the rapes, I don't mind most depictions of sexual assault in the manga. But I do think Casca’s situation is unique. She’s sexually assaulted significantly more than any other character in the manga. Are those scenes all needed? No. I got the idea pretty early that Berserk is a brutal world, thanks.
But yeah, I definitely prefer the way the anime gradually introduced the threat of the supernatural, it feels and flows better that way, and the open ending was perfect to make you want to read the manga (crucial to why the fanbase outside of Japan exists in the firsts place). But a show has to work as a show, not cater to what came before and what happens after, or for fanservice of unneeded characters that are just gonna confuse the casual viewer. The important beats and the three main characters are fleshed out. Mood, atmosphere, pacing is mostly hitting on high levels. Literal adaptations don't necessarily mean quality, as they try to cram in as many information and plot as possible and it becomes a bloated mess. More often than not, limitations and constraints of time and money bring out great creative solutions if it's a work of passion, and also not discarding the importance of the deep involvement of the original creator (which clearly wasn't there in further adaptations).
I've shown Berserk 97 to many friends and watched it in every relationship I've been, and got almost all of them to buy the manga. I can only remember two people that thought the anime's omissions were important to the story. But the rest are probably just a bunch of casuals, not "true" fans, so what do they know.