I already asked the question in the post above. It's indicated that actually the messenger made the "provided Gateway" to Graendal's lair (at least not Moridin, who just appeared later and normally uses the TP). It's also strange that the messenger doesn't seem to follow Graendal through the Gateway, but stay in her lair. Apparently he awaits Graendal's return to Arad Doman and then probably closes the Gateway, after he returned through the Gateway to the Blight.

The answer to this could explain the zomaran's instruction to Carridin in TGH, prologue:
"You may change to your own garments if you wish, my Lord. None will see you depart here, nor arrive at your destination, but it may be best to arrive already properly
clothed. Someone will come soon to show you the way", i.e. basically how DFs from basically all over the world can quickly visit the Blight.

One explanation for this was that Myrddraal might be able to take DFs with them through the shadows, but maybe actually some of Ishy's servants have the ability or ter'angreal to create Gateways.

Besides that, I agree that the OP/TP usually seemed more obvious in the books.