Yeah, plug and play kits sometimes seem dim for two reasons:
1. Stock 4300K lights are slightly yellow, which offers better night visibility/contrast. When you go to a "whiter" (or bluer lol) bulb, the way your eye sees the light is different. Especially when you drive by areas lit by yellow street lamps and such.
2. The subimods kit is a plug and play kit, not a HID retrofit. That means you're using an HID bulb (HID's function kind of like flourescent bulbs and have a different light output shape) in a projector lense designed for incandescent bulb light output shape. A lot of your light's intensity will now be thrown closer to the car, instead of near the lense cutoff.
When you combine those two things, plug and play HID's just have much different performance