Hmm... it appears to me that your team has a pretty high Latios weakness. Given that Blaziken can't even OHKO it via Night Slash (252 Atk Blaziken (+Atk) Night Slash vs 4 HP/4 Def Latios: 64.1% - 75.64% - 2 hits to KO), and your team is in for it (yes, there's Jelli, but it normally doesn't take too much to KO that thing).
Let's go ahead and break down the team at a glance:
Garchomp / Tar / Rotom-W / Ferro
Change some of the sets a little, and you're golden. This core really isn't too bad, provided you have enough general Fighting-type counters (namely Terrakion, Scrafty, Hitmontop, Conkeldurr etc.). Also, with a slight tweek to Ferro, you would actually already have two Latios counters (note, that doesn't mean you have two Dragon counters).
That leaves Jelli and Blaziken. Looking over your team, I heavily question their use here. In its current state, Scarf Thundurus-T might be a thing to worry about (which is the only common set seen besides Specs), considering many can be seen with something like TBolt / Focus Blast (I kid you not) / Hidden Power [Ice or Flying] / Grass Knot. Tyranitar can counter it since Focus Blast won't OHKO through a Chople Berry, but as far as everything else is concerned, keep your fingers crossed.
252 SpAtk Thundurus-T (+SpAtk) Hidden Power Flying vs 0 HP/4 SpDef Blaziken: 120% - 143.23%
Guaranteed OHKO
252 Atk Blaziken (+Atk) Flare Blitz vs 0 HP/0 Def Thundurus-T: 92.21% - 109.09%
56.25% chance to OHKO
252 Atk Fire Gem Blaziken (+Atk) Flare Blitz vs 0 HP/0 Def Thundurus-T: 138.31% - 163.64%
Guaranteed OHKO
In order for Blaziken to outspeed Scarf Thundy-T, it needs to be at +2 Speed, meaning the opponent could easily take advantage of that and proceed to pluck off Blaziken. As you can see, Flare Blitz is more than capable of denting, but again, it's all in getting to +2 Spe. in the first place. During Rain, Blaziken is dead weight. Tar can change the weather up, but in certain moments, your foe can easily predict a vital Tar switch-in for the unthwarted Flare Blitz and put the match in their favor.
248 SpAtk 30 SAtt IV Thundurus-T (+SpAtk) Thunderbolt vs 252 HP/0 SpDef Jellicent: 89.86% - 105.8%
37.5% chance to OHKO
252 SpAtk 31 SAtt IV Thundurus-T (+SpAtk) Thunderbolt vs 252 HP/0 SpDef Jellicent: 89.86% - 107.25%
43.75% chance to OHKO
252 SpAtk Thundurus-T (+SpAtk) Hidden Power Ice vs 0 HP/4 SpDef Garchomp: 118.03% - 139.89%
Guaranteed OHKO
252 SpAtk Thundurus-T (+SpAtk) Focus Blast vs 252 HP/4 SpDef Ferrothorn: 79.56% - 93.92%
2 hits to KO
I think the rest of these calcs speak for themselves when I say that Thundurus-T is a problem.
Going back to that four-core system and what your team is weak to, a member I would add is Scarf Salamence.