Don't confuse the road with the destination. They may look different on the surface but they should be taking people to the same brain states.
There are three primary or classical types of meditation and most kinds of meditation bridge off of that, all with different experiences, goals, and results.
1) Concentration meditation, like breath meditation. This increases concentration and mindfulness increasing awareness so one can notice subtle details they could not before, most notably the causal relationship within mental states.
2) Insight meditation, like noting meditation. These kinds of meditation are used with the teachings to get enlightened, but ones mindfulness and awareness must be high before being able to yield any fruit.
3) Metta meditation. It's where you wish for good things to yourself and others. This can help cultivate positive psychological states like metta (loving kindness) and compassion.
4) Zazen, which is technically a kind of concentration meditation, is a kind of meditation where you copy the posture of the teacher in front of you mirroring their movements rounding out breathing patterns and what not. It's often a do for nothing good for nothings meditation.
And more...
Most people don't meditate correctly or go deeply enough to enter the breathless state. A lot of the popular teachers of mindfulness meditation (Kabat-Zinn, etc) never mention what happens when you allow your body to become totally still and ignore sensory input (or even that you should). Yet this leads to the Taoist's Original Breath, or Patanjali's spontaneous Kumbhaka, where the breath naturally suspends for long periods of time, and is really the doorway to deep meditation.
Sorry for people wanting medical science here - materialistic science has inherent limitations when trying to deal with subjective experiences such as the nature of consciousness itself. You'd have to convince yourself if you were interested that the states reached by e.g. intent concentration on the breath is experientially very similar to those arrived at by other methods.
BTW: I can see from your comment you've either never practiced Zazen, have no experience of it or have had a charlatan teacher.
> Fundamental awareness: A framework for integrating science, philosophy and metaphysics [1]
Satguru Bodhinatha Veylanswami recently quoted it and said it very much lines up with the Saiva Siddhanta perspective.
That seems to be the crux of the problem though... how do we know?