Yeah, I agree with you. I don't understand nearly as much about antennae as my brother, who is a HAM guy. My eyes glaze over when he starts talking about SWR and all that.
I think one of the issues with OEM vs aftermarket (TireMinder/TST and the like) is that our daily-driver vehicles don't have to deal with issues like distance and interference - at least not at much as an aftermarket TPMS. The OEM sensors are way closer to their monitor. On a MH with a tow'd, it could be a 30' or more distance without a repeater/booster.
Another thing is internal vs external. The OEM ones mount inside and look to be more stable than the ones we have whipping around at the end of our valve stems. No facts to back that up. Just saying....
Do your TM sensors have replace-able O-rings? When I change my batteries I always replace the O-rings. So far so good.
And when your sensor displays "bad info", what exactly does it show? (PSI is "off"/Temp seems odd/no information at all?)
Have you contacted TireMinder about the problems with your sensors? They were extremely helpful when we called for information.