I've never had an issue in checking in and boarding together with a non-status travel companion with TP; please note that I never ask if that is possible, I just do it. When asked any questions by the check-in or gate agents, I only say we're travelling together and they always oblige. I even managed to check-in together with a group of 7 people in the Premium area in LIS last July, being the only status pax.
By way of contrast, when I wasn't a status holder, but had a credit card which allowed me to check-in in the Premium area, I wasn't allowed to bringa anyone else and that restriction was enforced.
You seem to have a truly miserable experience with TP. Not everyone would fly the same airline so often if one would be or feel so miserably treated systematically, especially being a status pax.
My travel partner without status was sent back by TP staff in LIS at the boarding gate from the premium queue to sector C despite traveling with me and sitting next to me. TP staff seems (sometimes) to enjoy treating passengers unfriendly. The same goes for the random weighing of cabin bags and personal items with random weight limits as well as hiding in the front galley and not serving C passengers.
To your questions about why I still fly TP: This is a good one. I have reduced my flights with TP significantly and it is my last choice even behind Ryanair but sometimes there is no other option, unfortunately. Think of Europe-Terceira, FR completely stops the flights in the winter as there is no free-flowing tax money for FR anymore (while probably still for TP and S4). Sometimes I also need a day trip to FAO or OPO on one ticket. If I can though I avoid TP and also LIS as much as possible. Lovely city but a horrible airport, airline and management.
Unfortunately, it still is enough for status at TP as TP also hides mileage accrual in other Star Alliance programs or even gives 0 miles there while still giving a handful of miles in their own program.