TL;DR:
It's not hard to earn the ingame currency. No FOMO. Definetly not pay to win, since you get decent equipment, can unlock everything else with little time, it's a PvE Co-Op game with many difficulty levels to serve most player tastes. Buying ingame currency has some dark patterns though, but it's extremely better in comparison to other games with microtransactions.

Long version:
You can earn the paid (and sadly obfuscated) currency by playing the game and collecting some stuff. You don't need to pay at all despite the game's price initially.
It takes me about 15 to 30 hours to get enough of the paid currency in order to buy a warbond (the "battlepass", basically a package of weapons, tools and skins you get access to by buying such a warbond once). And that's me not even trying to farm the currency. I'm sure you can get there a lot faster if you're aiming for farming it.

It's also not pay to win. I understand the first impression, since it's actual different sets of weapons and armour which are locked behind it. But: on the one hand, you still have the standard warbonds which you don't need to unlock using that special currency; there, a decent collection of items is already present in order to find a style with which you can beat the game. On the other hand, it's a PvE Co-Op game with a lot of different difficulties to choose from. You can play it from extremely easy to very hard. It's not intended to be played solo. Although you absolutely can if you're good. That means: winning is easy. Even with equipment you don't like as much.
And let's not forget that it isn't that hard to earn the paid currency by playing the game. Unlocking the paid warbonds that way can be another incentive to play and get a feeling of progression.

What's also very important:
There is no FOMO. The warbonds stay where they are. You can complete any of them at any time in any order you like. Also, even in the ingame shop, there is not really FOMO: there are literally just four items: two helmets and two armours. Those switch every couple of days. But that switch is a cycle. Meaning, after some days those, you've seen on one day, are back.

The devs also made clear in a statement that they explicitly don't want that FOMO stuff and don't want it to be pay to win.

I have more than 200 h in the game and have unlocked every item in every warbond earlier than that. Never paid a cent. Not even for the game itself since I got it as a gift, lol. Also several of the shop items. (That depends on difficulty though. With lower difficulties might take longer.)

Yes, they are not "the paragon of microtransactions". First, because they still have microtransactions at all. Secondly, because it's obfuscated and superlinear (ratio between spent money and amount of received currency is not the same between the packages: you get much more if you spend a bit more). But if you compare that to other games, which employ microtransaction shit, it's waaaaay better and right at the top, after Deep Rock Galactic.