That's bullshit because there is no gore in the movie, firstly. Secondly, if anything, it was independent shock cinema. Of COURSE it's going to look "low budget", it's an indy horror from 1973 shot on a flippin' Super 8mm camera!!!!!
It was raw, off the cuff, and had such overbearing plausibility that you CANNOT deny the possibility that what was depicted in TCM could very well be an everyday occurance in some backwater town in the boonies.
The movie was FILLED with subtle visual "hints". Leatherface slamming the door and you have no clue what's going to happen next. That says so much more than watching him hack some poor kid to pieces. Scenes like that added to the mystery, the fear of the unknown, which is what drives true horror. Not predictable, cliched goings-on like in todays movies.
The content of the movie isn't what was scary, it was after the fact, when you finish it, thinking about how utterly realistic what we just saw very well could be. You don't even have to suspend reality in a movie like this, because you can percieve it as realistic. THAT is what makes a movie scary.