From my opinion, I don’t think ManaCube is pay to win. I know the owner(s) actively try to make the server as fair as possible.
Of course, people who purchase ranks will get perks and advantages - but I think this is understandable, as people who spend money to support the server don’t want to “waste” money. I would argue that most of the perks from donor ranks and crates are cosmetic (nicknames, shout, chat colours, trails, auras, customisable prefixes, titles etc).
I think since you can use cubits to purchase ranks and items in the new /cubitshop (on most gamemodes), it allows free-to-play players the option of getting the same perks as someone who purchased the rank, while not spending a penny. They worked hard, traded for and earned the cubits. Yes - you can purchase cubits on the store, but there are other ways to obtain them as mentioned above.
I think all players are entitled to their opinion; this is merely mines. I understand people have the view the server is pay to win, and while I don’t have experience on factions - this is my view as a whole. Things are constantly changing, and the server is growing. I would personally suggest trying out the server and getting your own opinion as at the end of the day; only you can decide if you like or dislike something.