Registered just to post this.
Most people in Japan have a traditional or out-dated mindset about commercial products always being better than doujins. There are various reasons to this I don't want to expand on, or know really well enough to be confident about what I'm saying.
Anyway, those who own games like Gradius and other commercial shooting games (sorry, I'm not really fond of shooters) tend to have a degraded view on the quality of doujin products within the same game genre. Touhou does not seem to be an exception.
I personally find this out-dated thought ridiculous.
I might be completely off the mark in this and my opinion might be nothing more than speculation based on subjective inferences about the games themselves, since I'm not too familiar with the Japanese fandom at all, so feel free to correct me if that is the case.
Could it be that such "elitism" towards the Touhou danmaku shmups has to do with the fact that they are
easier than most industry-standard Cave arcade shmups? I'm by no means a good shmup player, my skills are barely average and substandard most of the times (I haven't played them too much either, I've only gotten immersed in the genre via Touhou and I've only returned to it fairly recently after taking a break after MoF was released), but I've found that no amount lolMAME practice made me good enough to reach Stage 5 in Dodonpachi and ESPGaluda, but I've managed much more with most Touhou games in just a couple of weeks.
I personally find Touhou games much more enjoyable than Cave shooters, since the latter are much more about muscle memory (yes, much more than Touhou in my opinion) and twitch reflexes due to absurdly fast-paced danmaku, while Touhou feels more laid back and a bit more "strategic" in its patterns. However, I can see how people who are gods at Dodonpachi and the like can feel that Touhou is substandard in this respect--not that I share those impressions, though, since I believe the game stands with a style of its own in the danmaku genre.
However (and here is from where I take this previous idea from, so you'll see why I say it's completely subjective) I certainly feel such is the case with the Touhou fighting games. I'm a competitive fighting game enthusiast, to be honest, and though I'm not a really good player by Japanese standards, while the Touhou fighting games look nice and have some neat ideas here and there, they're completely substandard when compared to industry leaders such as Guilty Gear and Street Fighter, or even newcomers to it like Arcana Heart. However, the fact that Melty Blood was originally a doujin game by no means prevented it from garnering a
huge following in the Japanese competitive fighting scene, making it one of the usual games in the Tougeki SBO competitions.
I don't know, maybe I'm completely off the mark here. Feel free to shoot my argument down if that is the case.