Earlier, I mentioned that working on structure is Step One in developing IP, and is a precursor to making an aiki body. The first step of that process is learning how to align the joints so that you are not using dedicated muscle to hold your structure together, and so that force can easily be transferred in a clean "path" from point-of-contact to the ground, and back. Then, you learn to feel and manipulate cross-body connections from foot to opposite shoulder, and to manipulate tanden (dantien), meimon (mingmen) and kwa (not sure what the Japanese term is for that - the femoral joint and inguinal fold area) to receive/absorb and feed/project force both from within and that which is provided by a partner. These are not "stoopid jin tricks," but a methodological approach of systematic training in increments to condition and build an IP/aiki body.
Any authentic internal system has some kind of "dynamic stationary" standing exercise to work the foundational structure and connections, whether it's called zhan zhuang, tenchijin or 13 Points, or whatever. YMMV with these, as not all such exercises are created equal depending on the individual teacher, school and lineage; however, the general intention is to work the structure and connections. And as I stated, I have seen people start to develop structure within months, and be able to absorb a push and to neutralize a pull too. On an elementary level, certainly, with low-level stress from the training partner, but even so, it is the "stuff" of rudimentary skills and basic understanding, and will be built upon continually and forever. It should not take years if the person trains a little every day.
IMO and IME, that feeling of ease, balance and freedom of movement comes along after you've learned how to control your structure so that you are acutely aware of its position at any given time, and of any possibility of imbalance... and can adjust accordingly, without tensing up.