IROP days are going to happen, but the company can't plan to have additional staff for IROP coverage at all times. That being said though, sometimes management does drop the ball when they really need to call someone in. Or they actually have called extra coverage in, but the weather is affecting your major hub/just really that bad.
Safety is indeed always first. That means on days when it hits the fan, active flights in the air take precedence over those on the ground. When you have 4 flights diverting at the same time due to a weather event in your major hub, they should be safely handled before even touching a new release. They'll call looking for it, because its sunny in Vegas and where is my paperwork?? They can put the delay on staffing, weather, dispatch. It doesn't really matter to us. On days like that you just have to do the best you can. (and file an ASAP for workload!)
Day-to-day workload is hard to compare when you get to a major. Overall I'd say workload is about the same, but unlike at the regional level you get paid for what you're worth. At a major you may have less flights, but worse/slower software instead. Or different things going on like true international flights and ETOPs. Management is always going to want to staff as few as possible in the Dispatch Factory, and dispatchers as a group will always say they have too many releases. There's a balance to be found and it seems to bounce back and forth over time. Sometimes airlines will get too far from this balance and there are too many releases to be effectively flight following. ASAP tool is great for this, since it can become a safety of flight issue.