This.
With a full suspension it soaks up your uphill pedaling power like a mofo.
For the last two years I have been using my Ironhorse Sunday as a general purpose bike, riding down a paved hill you still have to pedal to maintain speed…its a fucking pig.
The Ironhorse Sunday is a downhill bike, meant for bombing down hills, stairs, whatever. Its built like a brick shit-house so weight is a factor too. I recently picked up a 2009 Specialized Hardrock for general riding. I got it used for $300, it has mechanical disc brakes as opposed to the hydraulic on the Sunday but they still work fine. I find hardtails much easier to ride than full suspension. Before I got the Ironhorse I had a Specialized Stumpjumper FSR (full suspension, hydraulic brakes, etc) even that would dog pedaling up hills.