Tadasana and Alignment are Not the Same
Before we start off on the wrong foot, let's just confirm that your mountain pose may be a beautiful tadasana, correct according to the lineage or style of yoga you practice. But a pose or posture is not necessarily neutral, and it is not necessarily aligned.
Tadasana typically expresses, with some variations according to style, as feet completely together, knee caps in a lifted position (tightening the quads), internally rotated thighs, pelvis swayed slightly forward, an erect spine, stomach in, chest puffed up (and forward), scapula pulled back and together, tension in the neck, arms, hands and fingers.
A truly aligned human body might look a little more like this : Feet the width of the ASIS and pointed straight ahead, thighs rotated to parallel, knee caps released, hip joints over ankle joints, a neutral pelvis (neither tilted nor tucked, swayed forward nor rotated), a rib cage that lives directly over the pelvis (rather than pulled forward and up), a vertical sternum, broad scapula, ears back over shoulders. Rather plain, rather neutral!
The tadasana-like tension pattern, relates to what Thomas Hanna called the Green Light Reflex, one that moves humans into action in the world. It originates as the Landau Reflex, a baby picking her spine and head up to take a look and begin the long journey of propelling forward through life. It is a call to alert and action and it's necessary to 'go get em'.. perhaps necessary to find a job, find a mate, embark on a big project, or to pro-ject confidence, power, success.
But we shouldn't live there, in that tension, in that posture. Seems obvious right? As someone who spent years working on and teaching what I believed was alignment, it took me a long time and some good teachers to recognize this. The 'alignment principles' presented to you in dance study or a yoga teacher training, are not necessarily alignment. They are postural preferences, esthetic ideals, ways to achieve poses, perhaps poetic ideas around movement, all inherited from our predecessors and culture. Alignment is what you do to the wheels of your car for the longevity of the vehicle's parts. Alignment of the human body, as described above, also optimizes human health.
Unfortunately, the posture we may have related to 'success' is also related to modern ailments - arthritis of the knee and hip, sacral or pelvic floor problems, low back pain, neck pain, low bone density, high blood pressure. After years of teaching yoga, I can often recognize the style someone has been practicing when they first walk up, based on their particular postural tension patterns. Residual tension still there, even after engaging in a steady practice said to unwind excess tension. This may be done consciously, again to present strength or beauty, or unconsciously simply because of chronic tension or particular arrangement of body parts. Scratch under the surface of the posturing, and there's typically something that's not quite working right, some pain or injury waiting to express itself.
I would never suggest giving up a yoga practice, it can bring with it so much benefit, far more than just physical rewards. But instead, just begin to contemplate if and how your practice may be creating or perpetuating ailments. How can you begin to incorporate alignment (based on physics rather than style or culture) into your practice and into daily life activity. This may mean that you don't focus endlessly expanding your ROM, nor achieving the deepest or most extreme poses, but instead on bringing bones, joints and all of the other living tissues into optimal relationship with each other. And remembering that no practice or exercise method can replace lots of everyday natural human movement.