Prior to Operation 5, classes were linked to characters. The following classes were known as:
Tactician - Keegan
Anchor - Mac
Blademaster - Lahni
In this video and at the time of this post I break down options 1, 2, and 4. At the time of this video, there is currently a 4x XP event running until January 4th, however, these methods are still superior to other ways of leveling. These methods will net you a great deal of Class experience ("CXP") and a good amount of Profile experience ("PXP").
One of the fastest ways to level up your classes in Gears 5 introduced after Operation 5 is to play with the mutators or difficulty.
1) Horde Frenzy - Overload - Master difficulty
2) Escape - The Surge - Insane difficulty with these mutators on More Filler Enemies, More Drones, More Health, More Pouncers, Ironman
3) Escape - The Clock - Master Difficulty
4) Horde - Jingle Juvies (until January 4th) Inconceivable difficulty
5) Daily/Featured horde/escape maps
To reach level 15 you will need to complete either 5 Horde Overload runs or 2 jingle juvies. Horde Overload gives you 21K CXP while Jingle Juvies gives you 42-46K CXP. These are by far the most efficient methods. Once the 4X XP event is finished I will update with newer values.
In terms of hours spent you’re looking at roughly 5 hours from level 1-20 for Horde Frenzy Master Overload and Inconceivable Jingle Juvies.