But if you have antigravity, why do you need wings?

(Same also applies to having force fields, but the whole “slow blade” vs fast blade thing is enough to at least handwave that away)

Possibly cost. But also suspensors only seem to give lift, or very small amounts of lateral thrust. All the pure suspensor vehicles we see move extremely slowly. It's possible the 'thopters use suspensors for primary lift, maybe 80% of vehicle weight, and the wings are just for manoeuvring lift and thrust.

The aversion to using force fields is more about their interaction with laser guns, when shot by one they cause an explosion equivalent to a small nuclear weapon. Not ideal to have wrapping a vehicle you may be flying in formation on an attack run.