First off, lets be real about something here: The only difference, effectively, between a "professional" and an "amateur" is, how efficiently they get the job done and whether or not they got paid well. To that end, realistically, no matter how "good a job" I do on my music, if I don't make money, people will call me an "amateur".
After decades of listening to and learning from different professionals in the industry, it seems they all have a different opinion on the "proper" way to produce music. I respect these people's technical talents for sure but I can't help but ask, if their way is so much better than amateurs, how come they can't agree on the best way to do the job?
With the exception of recording certain acoustic instruments, ever since the invention of the DAW, artists can fairly easily record, edit, arrange, mix and even master their own material. It's just a matter of time, patients and the talent to best utilize one's tools. So, in a way, has this rendered most professionals optional? Most of these professionals will cross their arms and tell an artist "your music will NEVER sound as good without professional mixing and mastering". I make the argument that this is only subjectively true.
Case in point: I just discovered that the old "crappy" stock apple plugin limiter in logic pro, actually works quite well utilized by my "amateur" level of engineering skill. Now, a professional mixing/mastering engineer, would probably tell me: It's going to make a difference using that old stock plugin on my 2-bus, instead of hiring some professional who has experience and access to really fancy advanced mastering limiters. And they are correct. It probably will make a difference in the sound.
The question begs to be asked though, how much of a difference?
More importantly, will the LISTENER know the difference? Will they even care? Will it change whether or not the song is good and whether the audience likes it? This is where most professionals will answer "if the audience didn't know the difference, then the top charting songs wouldn't always be professionally mixed and mastered. So obviously they can tell the difference". Professionals love to quote this correlation. However, they fail to mention the charts are all controlled/manipulated by big business through gatekeeping and MARKETING EXPOSURE. It's a well known fact that marketing and connections are the largest determinating factor to whether something gets on the charts or not.
So, you can probably see now, when the mainstream industry has the money/influence to push their professionally mixed and mastered music, it creates a VERY misleading correlation between "big hits" and professional audio processing. MANY songs in the past were hits, while having arguably WORSE production than what amateurs on a DAW are capable of. So why did it not matter back then but now magically does? The answer seems obvious, it doesn't actually matter. Not then or now. Baring extremely low production quality, the writing, arranging and performance are what make a great song. And the PROMOTION/EXPOSURE is what makes a great song successful/popular. NOT spending thousands of bucks so a professional engineer can make WAY MORE MONEY PER HOUR THEN YOU THE ARTIST LIKELY EVER WILL.
The elephant in the room seems to be, DAWs indeed DID make most professionals optional. Worse than that, in a way, it made a lot of them gatekeepers themselves. Where as before the DAW, you really DID need a professional to do most of that kind of work for you. Now, you no longer need them. So maybe this is why, though most of these professionals DON'T agree on the best way to get the job done, they DO agree on 1 thing: You the artist MUST hire them. Because professionals are indispensable. Well, of course they would say that. They would be out of a job if they didn't, lol. They'd loose money if they admitted: A talented artist can do MOST of this shit at home on a DAW, well enough at least for it not to make a difference beyond diminishing returns. For a modern music artist who writes good material, it's just a matter of talent and practice. You really don't need fancy equipment or a degree. Just a decent DAW, the internet and a mind capable of deductive learning.