Really annoys me when developers pull sh*t like this. It wasn't a glitch, wasn't a bug, was just giving players the ability to replay the mission if they wanted to. Not only does it discriminate against players who never had the opportunity to grind, but it's obvious they're doing it because people are making too much and it'll make buying GTA$ redundant.
You're not meant to be able to "complete" an online multiplayer a few days after it's released. Having the most expensive apartment, all the best cars fully modded, all weapons, clothing etc. unlocked. That's not how online multiplayer games work. The developers haven't pulled any sh*t. It's some players that have pulled the sh*t and are ruining the game for themselves and others.
Is it not rockstar's problem for putting the restart/replay option in?
I don't know the details exactly what's going on at R*, what was a mistake, oversight or what was intended. People will always find and use exploits. If it wasn't the replay it would be something else.
Developers need to be clear with the community, and let everyone know exactly what they consider an exploit as soon as possible so people know what to do and what not to do.
It reminds me of the saying "If it seems too good to be true, then it probably is". If getting money/levels in a game seems too easy then it's probably an exploit.