
It's called alternate paths. If you don't have what you need to clear them, it's your own fault for entering them in the first place. If you want to take a gamble with being ill-equipped, fine, but then you face the consequences.
The only "impass" that is not an alternate is Gate's Lab, which is the game's final stretch. And even that is a lot easier to clear than most players believe; I can't tell you how many fans to this day still think that an air-dash is necessary. By this point there is no excuse to not be properly equipped.
Generally, X6 is to the X-series what Lost Levels is to Mario. Low production value, highly challenging level design. Approachable, it ain't, but it's a great service for the hardcore fans. The game's level design is severely underrated by people who simply aren't up to the task of properly exploring it. There are tons of power-ups scattered, and rather than the brainless "use weapon x to destroy otherwise indestructible block y", a great deal of them require some good thought to reach, despite never once requiring a boss weapon. That is damn good level design that the series otherwise doesn't see, and it's a great and satisfying challenge to nab it all (without beating any bosses). The same can be said for the "impass" areas. You have to use your head, and pull out all the tricks for manipulating the engine that you know, and then you can find quite a few solutions to any given obstacle, and go with the one that suits you.
So not being able to get by as unarmoured X without any powerups whatsoever is good stage design to you? Also, I bring up the randomly generated museum stage that can very easily screw you over if you happen to go there first. That's not the only place either. It's not good level design when you need an
optional upgrade to advance normally, point final. I'm all for difficulty, as you should clearly know by now, but there's a difference between being challenging and not being able to advance without a freaking
optional upgrade. I'm repeating myself, yes, but apparently that's needed.