My opinions are complicated, but basically:
Those aren’t pronouns. They are complicated nicknames which change spelling depending on where you put them in a sentence.
Pronouns are a grammatical feature of a language which exist for the convenience of speakers. There are few pronouns, and you learn them all early on, and it is absolutely vital to their effective use that basically everyone who knows the language can recognize all of them instantly.
We could probably add a gender-neutral singular pronoun to English, and I think it might be useful to do so. But it would take significant organized effort and a generation or two.
But you can’t have a ton of “pronouns” where people are specifically inventing new ones to have one that no one else is using, because they cannot possibly work like pronouns.
In general, third-person pronouns are virtually never used by the people they refer to, nor are they used in conversations with those people. You refer to yourself as “I/me”, and the people you’re talking to refer to you as “you”. It’s only when someone is talking to someone else about you that the third-person pronouns come into play, and the purpose of those pronouns is to make their communication more convenient and effective.
Also, personally, I feel pretty comfortable in believing that people can have reasoned opinions on topics regardless of their personal identity. It makes sense to ask you to defer to or listen to the opinions of people with more direct experience, but there are aspects of this where it would make more sense to ask cis people about them than to ask trans people. For instance, trans people are going to be the experts on whether they feel that their experiences are being appropriated or mocked.
But you know what they can’t answer? They can’t answer the question “does this undermine the credibility of trans experiences with cis people”. Which is a real question, and a possibly-significant one from an activism standpoint. But if you’re trans, you’re not going to suddenly stop being trans because of some kids on the Internet playing word games. But if you’re not trans, and few to none of your immediate social circle are trans, you might be in a position where it was possible for something to make you more or less confident that trans people have real and meaningful experiences which they are trying to address by transitioning and requesting different pronouns. And that’s something that can only be answered from the outside.
Tumblr’s fascination with excluding people from conversations is really stunningly unhelpful.