Of course, all of that is still a work in progress, let's say it's at the state right now the Playroom was when it launched in English. The interface is mostly okay, but the rules are not available yet. There is a new client in development, tiflo space, which will in addition to other things be cross platform but will also be developed from the start with the English translation, thus all the rules and interfaces should work well. In any case to avoid going off topic too much, anyone can contact me privately either to report something wrong with the translation or simply to ask how to play a specific game and I'll be glad to help.
IMO winning for free is much better than winning for cash or prizes, because it brings out the bad sports in those who lost sometimes, including if there is a rank system, even worse. because then you could go "haha I have more quentins than you now!" and it would make a pay to win type which is not good. Maybe possibility we could take the ELO rating system or something similar for the more strategical of games?
Such a rating system already exists, look at the statistics for Chess, connect four, reversi and so on. However, I do agree it should be more obvious, and statistics perhaps better integrated into the client itself. I like in RS games that it tells you this is your 3rd win and so on, and you can directly see your wins and losses.
In RS they had issues with statistics as people played very short games so they could have more wins and thus get onto the leaderboard! Stats don't tell you amount of players in games, (much easier to win against 1 player than 4) easier to beat less experienced players, (stats don't show if player is new or just deleted an old account) and the length of a game can vary as already stated.
That's all true but statistics are still there because they are nice to have. They don't tell you that someone is the best but are usually a good indication. Besides the ranking system is quite good in Chess where the things you mentioned are not an issue. Statistics already exist, I was just talking about the integration into the client itself.