I have to ask: is fighting against (relatively) democratic states reasonable at this time? As long as russia, USA and china exist in their current form, there is no hope for a stateless society to exist without being crushed under the boots of a larger country.

Many anarchists would disagree with this. Anarchists strive to establish communities/stateless societies that are able to defend themselves against state repression. Many anarchists also believe state organized militaries to not be as effective in actually defending territory against invaders.

While not all examples are anarchist and successful, they all share libertarian ideals and are examples of libertarian communities defending territory against states / authoritarian forces. I think they should provide enough information to imagine an anarchist society defending itself:

• https://en.wikipedia.org/wiki/Revolutionary_Insurgent_Army_of_Ukraine
• https://en.wikipedia.org/wiki/Revolutionary_Catalonia
• https://en.wikipedia.org/wiki/Democratic_Autonomous_Administration_of_North_and_East_Syria
• https://en.wikipedia.org/wiki/Zapatista_territories