Read and learn the above ^.
Water does not cause rot. If it did, every orchid from a rainforest would be extinct, as they can stay saturated for weeks, if not months at a time. The true root loss process is suffocation.
Unlike most terrestrial plants that do most of their respiratory gas exchange processes through their leaves, orchids have evolved to do much of that through their roots.
When we water, the vast majority just pours through the medium. Some is immediately absorbed by the plant and the medium, but there is an fraction that’s the culprit- the water held between particles by surface tension (surface energy). If the voids in the potting medium are too small, that surface tension is strong enough to keep them full of water. That cuts of gas exchange air flow and the roots suffocate. (That is probably the reason the myth about “orchids must dry out between waterings” originated - let the crappy medium dry out and the airflow is restored…)
Use a coarse mix having larger voids and/or a medium that absorbs and wicks well like LECA, and those issue disappear.
One more thing. If you have an issue with one medium then change to another, don’t expect an immediate improvement. As roots grow, the cell structure “tailors” itself to function optimally in that environment. Once they have grown that cell structure cannot change. Move the plant into a different root environment and you have immediately rendered the root system sub-optimal, and they will start to fail, the rate of which is determined by the degree of difference between the old and new conditions. That is why the best time to repot any plant is just as new roots are emerging. They will grow to function optimally in that environment and support the plant while the old ones fail.