No, pay to win means you make a micro transaction to get ahead of the general audience by making a small payment of 'x' amount of currency. An example of a microtransaction may be subscription to a game, simple cosmetics or ingame items, or what the ignorant call "pay-to-win". However, there is a difference between DLC and items able to be acquired through microtransactions.

I would like to make a point that no warframe isn't pay to win in any way. Yes you can pay for some weapons. But those aren't by a long shot the best. The best weapons are only available through either doing missions or leveling up eanough to buy a blueprint and make it for yourself. Also it's a pve game you can't pay to be better you can only kinda pay to get a head start

Lol you don't even need money to buy at because unlike Destiny, Warframe has an economy.