Is Systema a modern version of Pankration? The ancient style is very loose in the rules. Except that for Systema, there are weapons included, it is also quite loose in restrictions and practical for serious combat.
Are all styles with few rules going to be similar to each other?
Pankration is an ancient form of fighting in competition. Participants wrestled, hit each other as hard as they could, choked each other, broke each others' fingers and other bones, and generally put a beating to each other in a manner similar to modern no-holds-barred matches. (Note the subtle difference between NHB and MMA--it's the difference between UFC 1-15 and UFC in the era of the Unified Rules.) Fighters often competed in both pankration and boxing. (Boxing, also, was a rather different and more brutal sport at the time.)
Systema is a modern martial art that involves little or no sparring until advanced stages of training. It involves no wrestling per se, no boxing per se, and competition is rarely or never emphasized. This is a fundamental departure from sparring- or competition-based training like Pankration or MMA.
There is zero historical relationship between the two arts. The two are only alike in that they are both martial arts; they barely share any similarities beyond that. One should also be careful: it is not uncommon to see Systema teachers who are pure charlatans, teaching fakery like no-touch knockouts and magical thinking. This is complicated by the fact that some of them used to actually fight, and may know how to train hard -- but the fact remains that all students should avoid bullshido.
Is Systema a modern version of Pankration?
Interesting, but no.
Pankration is a modern martial art recreation of an ancient combat sport introduced in the Greek Olympics in 648 BC which combined grappling and striking.
Systema (by which I'm going to make an assumption that you're referring to Systema Ryabko [Система Рябко], as taught by Vladimir Vasiliev, or Systema Kadochnikova [Система Кадочникова, or its better-known-in-the-United-States off-shoot, Systema Spetsnaz (Система Спецназ)]; I can think of half a dozen to a dozen other styles from the former Soviet Union that are called Systema), is derived from a number of different traditions, including folk wrestling traditions, as well as Cossack warrior traditions.
One fundamental difference is that Pankration (as practiced nowadays) is a combat sport, where Systema (as defined above) is a system of combat designed for military use. While Pankration may have few rules, it does, at its core, have rules.
Are all styles with few rules going to be similar to each other?
Unfortunately, when you look at the big picture of all arts, they're still fundamentally tied to the artists using them: we all have human bodies, and thus are restricted to human body movements. In this way, the broad strokes of all martial arts will always appear the same to a person with little or no experience in them.
Keep in mind Pankration maybe used in competition but the competitions are still fought on Marbel floors in Ancient Greece! Pankration is still commonly labelled as the deadliest form of martial arts in the world the kicks are meant to break ribs, the grappling moves are meant to break bones or at least dislocate and break tendons.
Pankration is not a competition sport similar to MMA. The form taught for competition is the same one as used by both Greek special forces as well as an optional advanced forms in US branches of the military. Look up the Marines vs the Army Pankration matches.
