Lots of good points and I agree with much of it. I brewed for close to 15 years without entering any comps. I kind of refocused my brewing at that point (most of my brewing to that point was mediocre, inconsistent, etc). I entered a few comps and kind of ended up all over the board..... I had some good ones that did well, others that scored poorly and I got some good feedback. It actually really helped be focus in on my brewing and I explored new styles and gravitated toward 6-10 styles that I really tried to perfect over a 2-3 year period. In the end, it made me a much better brewer as I entered many comps with the same beer, got lots of feedback, tweaked my recipes and processes...... It made a big difference for me for sure. I live quite a ways from any large home-brew club, so it was kind of good way for me to get that type of feedback I could not get another way.
I enter some here and there, but not as many as I used to. At the most, I was probably sending 4-6 entries to 10 or 12 comps. per year. Entering the same beers, or different batches of same beer, many times really allowed me to ignore outlying comments and look for consistent criticism or praise.
To me, there are kind of 3 reasons to enter comps -
1.) Feeback/Evaluation - if you are doing this, you almost really have to enter a lot. Now that I enter comps sporadically, I really find the "feedback" sort of worthless to some degree because I am getting one set of sheets, on one beer, one time..... and that is it. You need many perspectives, and you need to be an active participant in reevaluating your beer with the feedback you get and rebrewing the beer multiple times for more evaluation. In my opinion, that is the only way the "feedback" concept is going to pay off.
2.) To win.... that is why they call it a competition. Whatever the motive..... pure competitiveness, medals, some great prizes that are given out.... Nothing wrong with entering just because you are trying to beat people.
3.) Fun and to support home-brew clubs and local organizations that are hosting. Some contests are fund raisers for a cause, some are fundraisers for homebrew clubs, some are just a way for a bunch of people who like beer to get together and talk beer. This is a good enough reason to enter as well.
In the end, even though there are good and bad judges, and even though it is still subjective it isn't all "blind luck" either. Blind tasting of a decent sample size of your beers can tell you (in general) if you are consistently producing very good beer.
If you enter 50 beers in big comps (I am talking 300-400-500+ entries or bigger, the ones run by big home-brew clubs with lots of support, and lots of solid judges) ..... people who consistently brew very good beer are generally medalling somewhere in the 33%-50% range over 50+ entries, and spaced out over a 8-12 different comps. And, they are probably also getting low to mid 30's (or better) on almost all of the beers they enter. From my experience and observations, if you really want a "blind" validation of how your beer stacks up, that would be a pretty good benchmark.
*** OH, my favorite feed back of all time (from a well known Master Judge): On a british ordinary bitter - "Faint vomit notes initially...... fades quickly, however, and quite nice after that." Scored something like a 34 or so. And, he was right..... it did smell a little "vommity" on first whiff