Sechel:
If I said telling an Ashkenazi he can eat kitniyos on Pesach is a “serious issur,” would you accuse me of “being disrespectful to Sphardi poskim?” I didn’t think so. I never said anything against the Baal HaTanya, but trying to get people to abandon their minhagim and adopt ways that can be considered assur by their actual minhagim is a big problem; you keep screaming discrimination to avoid dealing with that reality.
The tefillin size thing I mentioned is brought down in Mishnah Berura (authored by the Chofetz Chaim who, in your mind, loved the Baal HaTanya so much he thought we should all ignore our minhagim and become Lubavitchers). However, I believe it’s straight from the Machaber. I think Chabad is alone with the jumbo tefillin shitta. I did actually learn Shulchan Aruch HaRav on hilchos tefillin (I remember specifically because he writes a good argument, ironically, on why we SHOULD wrap during chol hamoed). I do not recall any mention of the giant dimensions, but I will look.