As you already stated dragons are problematic to this team, and its quite obvious since you dont have anything to take outrage or dmeteors. Heatran is also quite problematic, basically it walls everything on this team, and if you face the one that can outspeed Landorus you are going to lose. I agree with eranu with his change of Scarf Jirachi, but try this spread: EVs: 108 HP / 252 Atk / 148 Spd with a Jolly Nature. Since this is your only steel, you are probably going to switch on rachi basically against every dragon, and the added bulk lets you take less damages from Lo Draco meteor or Outrage of Cb Dragonite. You dont lose that much in term of speed, you still outspeed Adamant scarfmence, running max speed jirachi without genesect in Ou is not that usefull anymore, and you really need some bulk.
Now to fix your weakness to Heatran, i think you can change your volcarona and venusaur set. On venusaur you really need Earthquake to avoid being fucked by heatran, as almost any Sun team without Dugtrio. Since you need to use Earthqauke, you can as well change your hidden power fire to ice, getting more coverage. Earth+ice is one of the best coverage in the game, and its a way better than the poison stab. Hp ice lets you beat Scarfmence or Dragons locked into Outrage. Now you should also change the spread on venusaur, Modest surely lets you hit harder but the point of clorophill is to outspeed everything, so you should change your spread to outspeed scarf latios, which can be a problem otherwhise. EVs: 80 Atk / 252 SAtk / 176 Spd with a Naive Nature is what i use on my venusaur. The speed lets you outspeed Scarftios and the rest of the speed is on Atk to do more damage with Earthquake.
Now on volcarona i would put Hidden power Ground over Giga drain to hit Heatran harder. Giga drain doesnt help with everything here since politoed is already fucked by Bug buzz and Keldeo cant do a shit with sun up. Im not sure anyway that life orb is a good item without giga drain anyway, i think leftovers is better, witj life orb you are probably going to be stalled out some turn since a priority can finish you, and volcarona is already powerfull with a +1 with the sun so you wont miss any important ko. Also, if you change life orb make sure to put FIre blast instead of Fiery dance. Thing is, +1 fiery dance hits like a +0 fire blast, and considering fiery dance only has 50% of chances to activate i think you are going to lose time trying to get that boost since fire blast have more immediate power, also i dont think your opponent lets you spam random fiery dance.
On starmie, i think you can put recover instead of thunder and a more defensive spread to tank better keldeo's hits. Ninetales wont switch into it and Venusaur doesnt like to take damages with rain up, so starmie is your main answer to it. It also helps a bit stalling heatran in case you need to, with a max hp investiment starmie can recover 8 times stalling the heatran's fire blast and it can also recover on Lava plume of defensive Heatran. Thats it, hope i helped!
Summary of changes:
: Jirachi @ Choice Scarf
Trait: Serene Grace
EVs: 104 HP / 252 Atk / 148 Spd
Jolly Nature (+Spd, -SAtk)
- Iron Head
- Ice Punch
- Fire Punch
Giga drain --> Hidden power ground
Fiery dance--> Fire blast
Life orb --> Leftovers
Sludge bomb --> Earthquake
Hidden power fire --> Hidden power ice
Your current spread --> EVs: 80 Atk / 252 SAtk / 176 Spd with a Naive Nature
your current spread --> EVs: 252 Hp / 4 Def / 252 Spd Timid Nature