The body weight differential is minor. The real weight issue is the size of the sensor — and the diameter of the lenses required to focus an image with the same angle of view on the sensor. Want a lighter system? Switch to a smaller sensor, if you can deal with the hit in low light performance

That said, there are two reasons I can think of that someone starting out might prefer mirrorless

• histograms before a shot is taken (with a DSLR, you need to use image review to see if you’ve nailed exposure)
• eventually all interchangable lens cameras will lack mirrors — just because an optical viewfinder is an expensive, delicate apparatus, as is a shutter.

Speaking of shutters, most mirrorless cameras still have mechanical shutters, most of those (up to full frame) are bladed shutters just in front of the sensor.

The reason to prefer DSLRs I can think of:

• apples-to-apples (same sensor) they are a good bit cheaper than mirrorless right now
• batteries last a lot longer — if you’re carrying one for an extended period away from power, the body weight differential is easily surpassed but the additional batteries you have to bring along — and this is exacerbated in the cold
• Although mirrorless is catching up, they focus better/faster in low available light