Do squads lose order levels by class swapping?

[Xtrasweettea]

Changing classes does the following:

• Lowers their current EXP and causes them to lose levels
• Changes which attributes they can offer for missions

What doesn't change:

• The tactics and ranks within those tactics that squad member earned. So that squad member will not lose that Offensive 5 for switching that Marauder to another class.

As for your bonus question:
It counts on how fast you want to clear the content with them.
GLD, even with offensive 5, does really poor damage. Though it is a tradeoff for them being able to grab hate a bit easier.

MRDs on the other hand, with 5 offensive will be able to out damage almost all of the other DPS squadrons, even with them being offensive 5 (Rouge I knows will overtake MRD damage). Of course, they have a slightly harder time grabbing hate.

There is a way around the hate grabbing issue: don't use engage. Instead you pull with a range attack of some sort. The enemies will converge on you, and either of the tank should have an easier time grabbing hate off of you.

My team I use for quick dungeon runs are:
Marauder, Rouge, Rouge, and me as WHM. All squads have Offensive 5. I can easily get 13 minute dungeon runs out of them on the dungeons that don't have that many quirks.