I think blissey and heracross hurt this team a lot more than you give them credit for.
Blissey isn't threatened at all by roserade. Yes you can put it to sleep and then start setting up spikes but spikes can be spun away later. I know gengar can be an antispinner but I'll address that later. Unless you get some freakish long sleeps, it can wake up and seismic toss/ice beam and put a serious dent into roserade. It also doesn't change the fact that blissey walls roserade and you can do nothing but switch if spikes is already out.
Gengar obviously does not touch blissey. Taunt heatran also is shaky against a blissey. You can taunt to stop it from using softboiled pretty much but fire blast is a 4hko at best and that's only if you get on the high end of the damage spectrum and don't miss on any of them. Meanwhile it can 3hko you with seismic toss. You've got explosion obviously but I get the feeling that you'd rather not sacrifice heatran to kill blissey while you've still got hitmontop and lucario in play. So that's another pokemon to be switching out against blissey.
So that's more than just 1/6 pokemon that are stopped by blissey. I mention this because blissey can easily come in on these pokemon and then just seismic toss the switch in and slowly wear you down.
You also fail to address the heracross threat adequately in my opinion. In the threat list you don't mention any specific ways to counter it other than to say that your pokemon can "take care of it". I'm curious as to which pokemon handle it and in what way? Because at a glance, close combat hits 5/6 of your pokemon hard when they try to switch in on it and they have no way to recover the damage. Gengar is obviously immune but still is hurt by a predicted stone edge/night slash. I won't go into prediction, however, seeing as that's uncertain ground. But with only 1 rather fragile pokemon being able to switch into 1 of its main moves, it leaves pretty much no room for error when it comes to switching into heracross. I would have to say you should add more than just a "my pokemon can take care of it" to the threat so I can get a clearer idea of how you actually take care of heracross.
On the topic of gengar, I feel that being a scarfer, it is made to handle a lot of the threats that your team would otherwise be unable to handle. It's something that is probably protected a lot of the time as its death could cause a lot of your team to fall apart. 2 of its roles I've mentioned above as antispinner and heracross switch in. So my question is, how does your team do after it is killed by pursuit?
If your opponent has a weavile or ttar with pursuit, its death is almost unavoidable. If you don't know they have them, you can't really predict and use focus blast so they can come in fairly easily.