Can you imagine how much momentum would be lost if Guts would fight Wyald and win just a few episodes before we got to the Eclipse? The insanity, shock and danger of the finale would deflate significantly. Do we need Casca to go through the same shit, but worse? Who cares if we need to see that Guts can kill an apostle? We've been witnessing countless times how his strength is beyond any human.
I disagree. I think it lulls the reader into a false sense of security before slamming them even harder in the face. And I think the ordeal of that fight, where Guts gives everything he's got and barely manages to almost-but-not-quite-win, serves as an important step for him becoming the Black Swordsman while also underlining how insanely desperate their situation is during the Eclipse.
You say we don't need to see this or that, but it's not like we're riding the bus to get to a specific station and every stop in-between is a waste of our time. It's all about the journey. Otherwise reading a one paragraph summary is enough. Not to mention that if there wasn't any clear progression in Guts' abilities before he becomes the Black Swordsman, people would rightfully call it an abrupt transition.
And I don't want to get into a protracted discussion because I'm not looking to convince you, but those scenes are also chock full of little bits of character development between Guts, Casca, Griffith, and even Judo and Pippin. This stuff is all great to me, it's top notch Berserk. It expands the world and makes you love those characters more. Even Wyald is great as the basest, vilest possible villain you can find. Completely grotesque and undignified, literally a horny monkey that embodies the loser apostles so that Zodd or Locus can be the cool ones.
Of course, if you're approaching this from the perspective that the anime's ending comes as a big shock, it's another matter entirely. As an advertisement for the manga, it worked great the way it was done. But if you compare the two "versions" of the story, there's absolutely no contest at all between them as far as I'm concerned.
But of course if they had a big budget and more time they would've adapted it closer to the source material, but that doesn't always mean it's a good thing, there's a myriad of examples of that when translating to different media.
The varying merits of adaptations is its own topic. In this case, the 97 anime certainly achieved its goal with great success at the time it was made. Despite its low budget and the difficulty of adapting the source material, it managed to be compelling, respectful and, through its almost revolting cliffhanger of an ending, drove people to the manga. Far from me the idea of denying that. But it was also a product of its time, and I don't think it's unreasonable to say that a better adaptation could be produced for Berserk today if someone were willing to invest the appropriate budget and talent. Anyway, for what it's worth, I personally don't feel a need for more Berserk adaptations.