first things first @ leftiez
252 Atk Choice Band Terrakion Stone Edge vs. 212 HP / 228 Def Latias: 211-249 (59.6 - 70.33%) -- guaranteed 2HKO
that was with your physically defensive latias EVs from CB terrakion, you calculated that wrong. I used the honkaculator 4000.
252+ Atk Salamence Outrage vs. 212 HP / 228 Def Latias: 384-452 (108.47 - 127.68%) -- guaranteed OHKO
This team is solid but if defenitely has its weaknesses, mainly fighting types and trapping. This team can't handle calm mind latias if scizor goes down and scizor can't take on HP fire variants although rotom could paralyze so U turn is faster than hidden power fire but if scizor goes down or you get over predicted with the pursuit you will be swept. Heatran is set up fodder, rotom and xatu are set up fodder, +1 Latias will beat yours usually and choice scarf terrakion could be handled easily by other team members as well as latias can take a hit decently well and hit hard back so long as sandstorm is not available. Latios falls in the exact same boat except calm mind latios is rare and does not always carry recover and scizor and terrakion can revenge kill it much easier. Likewise, if Tyranitar traps latias a keldeo which is often paired with the tyrant could be waiting to sweep you clean, although xatu might me a slight roadblock if it is healthy. Much like HP fire latias calm mind keldeo could often sweep you anyways because it will always win the calm mind war against latias. Rotom-W will help a LOT here but I will show why it isn't perfect below.
Rain teams are a huge threat to you. A standard Politoed/Ferrothorn/Keldeo/Tornadus-T/Jirachi/Tentacruel or something of that nature will really prove troublesome. Because of this my first suggestion is that you use will o wisp on Rotom to burn ferrothorn which is its main roadblock versus rain. Yes Xatu can take on most ferrothorn but having it slowly dying is much better than having it sitting there alive in a stalemate with xatu. Note that against rain teams rotom-w is your main player with everything else performing a niche role occasionally. So running will o wisp rotom is definitely a good idea here. While it will not move mountains it will do something. Another thing I might try against rain is a LO starmie or bulky starmie over xatu. Starmie helps against rain although ferrothorn is a bitch unless you can burn it with scald. Starmie provides another water resist and is not weak to terrakion stone edge. A last option is defensive tentacruel over xatu who can set up toxic spikes or provide toxic support for latias to possibly muscle past pink blobs. Tentacruel and starmie are both also back up keldeo checks if latias does fail which it very well could.
Will O Wisp over Thunder Wave
over Xatu. I can give you sets if you want, but I think you can pick sets you like.