Maybe it's just a difference in perspective, but I don't think it's reasonable to expect pilots on Vatsim to perform to the same standards as actual instrument rated pilots.
However, the exact opposite is expected for controllers.
Your comment of "It's a game. Games are supposed to be fun" is only
mostly true. Games have rules. When people don't follow the rules of the game, the game is not fun...it's unfair. The rules on VATSIM are very clear (CoC) and are intended to keep realism at a high level. For pilots, the key rules we are talking about here are in B8:
B8(a) A pilot must be familiar and proficient with the operation of their aircraft prior to connecting to the VATSIM network and shall comply with all agreed (read-back) air traffic control clearances or instructions. Where unable to do so, such as where operational safety is compromised (e.g. TCAS conflict resolution), air traffic control must be notified without delay.
B8(b) A pilot is expected to undergo reasonable preparation for their intended flight and potential diversions. This includes basic familiarization with arrival/departure airports, departure/arrival procedures and their planned route. This includes familiarization with airspace structure to prevent infringement of controlled or restricted airspace.
B8(c) A pilot shall be expected to promptly comply with basic air traffic control instructions that are applicable to their flight rules. These include:
(1) Holding position on the ground at an airport
(2) Flying a speed, heading, altitude or flight level
(3) Approach to land, either visually or flying an accepted instrument approach procedure
(4) When IFR, fly a cleared route by use of navigation aids / waypoints and fly to unplanned navigational aids / waypoints when instructed
(5) When IFR, fly a holding pattern
The expectations are clear. The rules are clear. The "FUN" level for controllers and pilots alike is tied directly to everyone following these rules in the VATSIM CoC.
Does it take practice? Yep. Is this stuff generally hard and complex to someone who doesn't train IRL for either a Pilot Cert and Instrument Rating and/or an ATC specialist job? Yep! But with the VAST resources (free and available online), along with time and patience, the skills are learnable -- both in the virtual flight deck and behind the virtual scopes.
And, I respectfully submit to you that taking the time to do it right and to play by the rules instead of just hacking through it, is VASTLY more rewarding!