I travel air Canada 30+ times a year. GTE strictly means what it says - you don't have seat assigned and you may get one at the gate. They cannot help you at the checkin until they know who all is boarding. So from that perspective strictly, I understand that sending them to gate to await their destiny,rather than try to resolve at the checkin counter. At the checkin,you are a Schroedinger passenger - just don't know if you'll make it or not. There's nothing they can do to you there.
I do not believe it is correct to imply that GTE absolutely means you WON'T be boarded and thus its a complete lie. I have had that on my pass and have boarded - granted I have a bit of priority (lowest status level). Colleagues without status have had same experience. You just don't know.
Article also doesn't advise strongly enough to do an online or early checkin.