Like so many conversations, people are confusing is with ought.

Is:

"Dude" is gender neutral if used as a discourse marker because discourse markers aren't about addressing a particular person, but used in managing the flow of a discussion. It shares commonality with words and phrases like "well," "oh," "I mean," "I guess," "yeah," and so on. Notice how words like "man" and "bruh" can also be used as discourse markers. I suspect what happened was dude/man/bruh was originally just a way to address a male listener and through grammaticalization, it acquired an additional use as discourse markers. But the older way of using dude/man/bruh in order to address a male listener still exists. Ultimately, it's the difference between saying "man, let's get something to eat" and "man, this room is so big." But even then, there's also ambiguous cases like, "man, I'm hungry" which can go both ways as either a discourse marker "man, I'm hungry, I shouldn't've skipped breakfast" or directly addressing a male listener "man, I'm hungry, let's go out to eat."

Ought:

"Dude" ought to not be used as a discourse marker because there are ambiguous cases which causes confusion whether it's being used as a discourse marker or as a form of address. The consequence of this confusion is that non-male people risk being misgendered. It also can be weaponized by transphobes as well. I would say the easiest words to replace them with would be either "homie," which strictly speaking came from "homeboy" although "homegirl" has long since been adopted as well, or "cuz" from "cousin." The main obstacle is that both words are from AAVE and should these words be adopted for general use, it's going to be yet another case of non-Black people stealing words from Black people.

However, it's not just the case of not using "dude" as a discourse marker. It has to be replaced with another word. And in a sense, "dude" itself was the replacement word for "man." "Man, this sofa is fucking heavy." -> "Dude, this sofa is fucking heavy." But what does man/dude/bruh convey in those sentences? I suspect it's to be emphatic, the English equivalent of Japanese よ. Consider "this sofa is X," where X can be any appropriate adjective (heavy, cheap, brown, and so on)

To hesitantly or cautiously express that the sofa is X:

• I guess the sofa is X.

• I mean, the sofa is X.

• Uh, the sofa is X.

To emphatically express that the sofa is X:

• Man, the sofa is X.

• Dude, the sofa is X.

• Bruh, the sofa is X.

To make the sentence sound more natural, you add an appropriate adverb before X to get:

To hesitantly or cautiously express that the sofa is X:

• I guess the sofa is kinda X.

• I mean, the sofa is kinda X.

• Uh, the sofa is kinda X.

To emphatically express that the sofa is X:

• Man, the sofa is fucking X.

• Dude, the sofa is fucking X.

• Bruh, the sofa is fucking X.

Perhaps it's because man/dude/bruh originate as words for addressing men that it acquired its alternative use as a discourse maker used when you want to sound more assertive.