I take your point and I think it's a fair one. On the other hand, I think there is such a huge gulf between "published" and "successful" that there has to be an opportunity for people printed by small presses, or indeed anyone not published by the big outlets, to have a go. And, given the bad way that publishing currently works, that would include a lot of writers.
Strange as it may seem, I don't feel like a professional, or a success. I would feel professional if I wrote fiction as my job, and I would feel successful if I was making a decent amount of money from it - by which I mean about as much as you get for simple manual labour in a supermarket. That may or may not be fair on new and struggling writers, but there it is. Without doubt, I'm very happy with what I've achieved so far, but it doesn't feel like enough, fairly or not.
Also, I may be a successful published writer - depending on how you define it - but I am definitely not a successful self-published writer. There are people who have never been near an agent or a publisher who sell far more and make many times what I make (probably in my day job too) from self-publishing. I am a pre-internet person, I'm not into fandom and I don't like or have much affinity for promotion. I have probably made my money back from self-publishing, and that may be because I got a discount on the cover art. What being published traditionally has probably done is to enable me to tell people who liked the traditionally published books (which are very different indeed) that I'd written a fantasy novel. That's not to be frowned at - it's undoubtedly helped me, but not as much as being liked/hated/etc in geek circles would have done. Say someone from Critical Role self-publishes a fantasy novel. The traction they'll get from that would be hundreds of times more powerful than my previous efforts could ever do.
There was a case a while ago where quite a known author (within the genre, but not a household name) entered, and did okay, but not especially well. IIRC, there was a bit of muttering about whether this was reasonable, but it seemed to come down to (1) nobody had said that she couldn't, and (2) she hadn't published much for a while, and so it counted as a new venture for her.
I suppose what I'm saying boils down to the fact that being traditionally published in some form doesn't mean all that much in practical terms (although it meant and still means a lot psychologically to me - it was my chief ambition since the age of 12 or so). Thirty years ago, someone like me might well have had a small but steady career, putting out books steadily and making a reasonable amount to top up my usual earnings. Because the mid-list has disappeared, that doesn't happen now.
Ideally, there should be some sort of cut-off point, but I think it should be about earnings (say, no more than £10,000 pa from writing), which would be intrusive and basically impossible to enforce. Other than that, I'm not sure.
