There are more differences between GTA Online and GTA RP than one might realize.
Some casual fans would assume that GTA Online and GTA RP are the same. However, this couldn't be further from the truth. There are many differences between the two games (although it should be noted that there are several GTA RP servers, so it's technically a lot more than just two games). Some differences are minor, whilst others are major.
The most noteworthy difference is that GTA Online is an official game made by Rockstar (technically a part of GTA 5). By comparison, GTA RP isn't just a single game. The most important distinction is that all of the GTA RP servers are fan-made. Of course, that isn't to say that there aren't some similarities between the two types of GTA games.
GTA Online vs GTA RP: How different are the two games?
There are numerous differences amongst each individual GTA RP, so comparing it to GTA Online is a daunting task. Still, it would help to compare the two games' similarities before discussing the differences.
Both GTA Online and (most) GTA RP servers operate on the GTA 5 engine. Hence, players familiar with the physics of GTA 5 will understand how most GTA RP servers work, just as they will with GTA Online. However, that isn't the only similarity between the two titles.
Another similarity is that both games promote customization. Whilst GTA RP is more robust in how it approaches customization, one cannot argue that GTA Online is lacking in terms of clothing options. Compared to other GTA games, both GTA RP and GTA Online allows players to create and play as their own protagonists.
Both games also have a huge focus on multiplayer interaction. As both games are played online, one should expect to see other players acting on their own accord within the open lobbies. It should also be stated that most GTA RP servers share a similar map to GTA Online's, given that they both use the GTA 5 engine.
The differences in roleplaying and story
Of course, GTA Online isn't GTA RP. While people can roleplay in GTA Online, the vast majority of GTA Online players do not roleplay. Instead, their avatar character is just a model they look at, often being a reflection of their own desires.
Part of the reason GTA Online lacks roleplaying is because there is a set storyline players can follow. While they can choose the order of several important missions and heists, the important thing to note is that GTA Online only has so much story a player can see. If one player watches another beat GTA Online in its entirety, then they've seen everything there is to see.
By comparison, GTA RP has no set stories in the games' code. There are stories pre-established by other real players, but it's also something the whole community could influence. That's not even mentioning how different the various GTA RP servers are from in terms of the overarching storyline.
NoPixel is the most popular server for English speakers, whereas Marbella Vice is the popular among Spanish speakers. Other than a difference in the language spoken, the OCs created by the two communities are different enough to have created different stories between the two servers.
They aren't connected to one another, so it's an example of how different stories can be in various GTA RP servers compared to GTA Online. Naturally, not all characters are tied to a particular story either, as some players can choose to create their own plots as they play the game.
Given that several GTA RP servers have notable differences in gameplay when compared to one another, some of them are bound to be strikingly different compared to GTA Online. Some GTA RP servers allow players to teleport to different locations for convenience, while this is not possible in GTA Online.
The most obvious difference between the two games is how Wasted and Busted works. If a player gets wasted on most GTA RP servers, they don't respawn immediately. Instead, they usually have to wait for a paramedic (played by another real player) to revive them.
Likewise, players don't teleport instantly when they get Busted. Instead, they often have to be driven to the relevant jail/prison, which means some shenanigans can take place. GTA RP's change in these two fundamental mechanics can make the game feel very different whilst playing it.
Different in focus
Perhaps the most obvious difference between GTA RP and GTA Online is the change in focus. GTA Online is all about grinding so players can buy the best equipment and items possible. As for GTA RP, most players treat it like a virtual life, where they can live out some wild fantasy.