Water bottle pockets can work well if you're keeping things simple—short tours, resort laps, or ultralight setups where every ounce counts. They're straightforward, easy to refill, and don't require cleaning a bladder system.
The trade-off is convenience and cold-weather performance. You can't sip while skiing or skinning without stopping, and in sub-freezing temps, bottles can freeze—especially at the cap. Bladder systems with insulated hoses let you drink on the move and are less prone to freezing when properly maintained.
If you mostly ride in-bounds or take quick laps where you can grab a drink in the lodge, bottle pockets are perfectly adequate. But for longer backcountry days or cold conditions, a bladder with insulated routing is worth the extra complexity.