To be clear, I am against paying IRL money or Arx for engineering unlocks or materials. Leave that stuff to cosmetics. That said, I am not sure I would consider it pay to win. If a new player hits the forums and coriolis to find the meta build all the cool kids and purple hairs say is the thing you need to get your murder on, and then pays to unlock the engineers and grinds the mats to build it, they are still a noob, and are still going to get murdered by anyone that half way knows what they are doing..
I am against it in principal, but there are times when it is a pita to run off to grind mats for a build when all you need is few more selenium or whatever to be done. I do have a moment of weakness where I think I would find it acceptable to buy mats while flying out to Hip 36601 to harvest mats and then running back to a mat trader. It passes relatively quickly.