Let's face it, GTA Online has a problem with the weapon selection system. This particular problem has been around for a good long while and is only ever getting worse with more and more weapons being added in the free DLC packs Rockstar keeps releasing. The most recent update for the game, Lowriders: Custom Classics added two new weapons, the double barrel shotgun and the compact rifle.
GTA V was chock full with various firearms by default and each update added a few more. With over three years of GTA Online, that adds up to a whole lot of DLC, which means a lot of guns. Now, AAA gaming has figured out prime weapon management systems years ago.
The weapon wheel has been widely used in shooters for at least a decade, but was around for a good long time more, but by now it has popped up in all kinds of games and settings. GTA V also opted for a weapon wheel when it comes to weapon management, however this system becomes a tad more complex when a large number of weapons make up the arsenal.

Usually, weapon wheels are separated into sections, based on weapon types. In games which have more than one weapon per type, the player is limited to carrying only one or a few of the weapon of said type. This makes your choice of load-out tactically important and makes switching between weapons under heat quick.
GTA V decided to take that working formula and toss it out the window. Instead, your Online character is carrying the full arsenal of weapons you have ever purchased or acquired in the game. Always. The weapon wheel is indeed sectioned off as per formula, however when you have several dozen guns per category and each time you open the wheel it starts from the very first gun in each category, you have a bit of a problem.
Cycling through 27 weapons in order to get the one you want in the middle of a gunfight isn't particularly advantageous — and yet GTA Online forces you to do this. Some people have managed to lock their favorite weapons of each category into default position in single-player, however certain situations will call of other equipment. Plus, this method doesn't usually work...