Let me better explain this, most HO teams stick to being either physical or special because as soon as the opponents physical or special wall is gone you can normally easily plow through their team. Sometimes a revenge killer also needs to go down for that to happen but for the most part it's: get up screens -> Try to break wall -> Try to kill their revenge killer -> win (or lose if you failed to do the first two parts). If you have a special sweeper and they keep their special wall for the special sweeper there can be an easy loss for you if at the end of the battle it comes down to say, Jellicent vs Keldeo
While it would seem smarter to have special and physical sweepers on the same team all it really does is make it so you have to break that side of defense with half of the possible team. Especially since you are using 5-6 sweepers (depending on suicide lead or not) you aren't going to be switching a lot due to the frailty of your team. When making a HO team you can't use the normal mentality of: if he brings out x I can just switch to Y because oftentimes you will either: lose boosts (and possibly not get them back), lose momentum, or possibly lose the mon switching in. HO tries to minimize prediction both in switching and the attacks you make. I'm probably missing stuff but what it comes down to is: you have 5-6 glass cannons. Switching is bad, overpredicting is bad, and splitting your team in half is bad. I'm not saying split HO teams can't work, it's just harder at times (especially against stall or defensive teams)