Depends on how you define "low standards". If you mean in terms of theming, sure, they're definitely in the lower tier by far. No argument here, and I would concede that Disney/Knott's/Universal are superior parks overall, no question. But in terms amount, variety, and intensity of ride, it's a pretty high standard--probably second only to Cedar Point, and best by far in SoCal in terms of extreme thrills. If I'm looking for intense speed and thrills, Twisted Colossus wins hands down against Space Mountain.
I mean, don't get me wrong... I'd totally love to see a beautiful looking, fully landscaped SFMM. But they're in a lose/lose situation here with both Disney/Universal/Knott's about an hour away... no matter what they do (say, for instance, they did put in all those tress), people are still going to shrug and say, "Eh, not as good as Disney/Universal/Knott's."
SFMM knows its lane and stays in it. In a market where it's competition are three of the top family/theme parks in the world, it has to offer something different the other parks don't have: extreme thrills and a cheap ticket price. And that comes at a cost of little to no theming, and a focus on the physical ride experience.