With respect to a fan who seems to know his stuff, Brian offered little in the way of artisitic guidance, and though perhaps the Beatles might listen if Epstein opined they could be a bit more focused & efficient in the studio, that's about as far as it goes.
Neither John nor Paul cared a fig for Brian's musical suggestions. Phillip Norman, in his book Shout! The Beatles in Their Generation, reports that once, Brian noted a bit too much tremble here or bass there. Lennon, over the intercom which all could hear, responded, acidly, "You look after the percentages, Brian. We'll look after the music."
Epstein didn't drop into sessions much after that.
Nonetheless, Brian Epstein deserves full credit for believing in the Beatles from the beginning, spending plenty of his own $$ to aid the group's rise (like buying up copies of their first single, "Love Me Do," helping to push it to #17 on the charts), and shaping their image with distinctive Pierre Cardin "collarless" suits, Spanish ("Beatle") boots, and even nudging them away from those awful Woodbine cigarettes toward the more refined Chesterfield brand.
He loved the Beatles, lavishing them with attention, indulging many a whim, and working tirelessly on their behalf. The Beatles would not have achieved the astonishing success they did without him.
Klein?
I won't expand, as he might sue me from the grave.
Lennon with the final word,