Here's another quick tip:
I mainly play Blast, so it's a little less helpful, but don't get obsessed with playing the same infantry class on every map, or even within 1 map
Like was mentioned above, use different classes at different stages of the match - that's what they are there for!
Use co-op (as was also mentioned) to level up the classes if you want, but mix-and-match the various classes as needed based on the current objective.
As an example, even with Co-op - I might start off as Specialist on the wide open part of the map, then switch to Officer or Infantry when it moves indoors, then switch to Heavy to hold the points at the end and let everyone have it.
And even within classes - you can change up weapons and star cards on the fly based on where the match is.
