So I feel like I might need to clarify on my original post a bit. That thought has mostly come from two aspects that I have experienced repeatedly. I mostly play trad games so it may be that the dynamics work differently with indie games where the balance of expectations/power dynamics are different.
The first aspect is the assertion that its ok for a player to not put in any time outside the session but that its expected from the GM. It just wouldn’t fly if a GM showed up with a rule book and they’d not read a single page of the rules. With trad games especially there is an unspoken expectation that the GM will, at a minimum, have spent the time to learn the game so I don’t feel it is unreasonable to expect the players to do the same. If they’re really adverse to doing it outside of the game then put some time aside during game time. Make it part of session 0 or set aside the first 15 minutes of a session to go over rules/make notes etc.
The second aspect is related to the actual play experience. I’ve run campaigns and listened to APs where even by the end of the campaign there was a player (sometimes more than 1) who still couldn’t follow even the base mechanics. So I could have been clearer in my original post - I wasn’t necessarily talking about complete system mastery but the core mechanics, such as how to make an attack roll in D&D or the specifics of the ability you use every session. Not knowing that 2 sessions in to a new campaign? Fine. Not knowing that 20 sessions in and having to get the GM to walk you through it again, not so fine (as you might be able to tell this is a personal bugbear of mine).
So directly responding to your question - Yes, I think a willingness to learn the system is a mark of a good player, especially in trad games where there is an assumption that the GM will be required to do a lot of work outside of sessions.
Is there a difference between traditional and indie expectations? Yes and no. I think indie games often do a better job of distributing responsibilities, which is helped by the fact that they also tend towards simpler rulesets. There is still an expectation though that the GM/facilitator/whoever brings the game to the group will know all the rules in advance and be able to teach them so you could run into the same issue of players not learning them over time.
Aside - I think it is also something where developers could do a lot to help by including core system reference/cheat sheets for the players - my experience with PbtA games is that while the playbook format can be overwhelming at first having a list of all the moves in front of each player is ultimately a massive help in grasping character intricacies.