Sorry I haven't been active. The past few days have been absolute hell.
Ttar over Terrakion is not wholly a bad idea honestly. The only reason why I chose Terrakion is because I felt faster threats such as Weavile, Tornadus, and certain boosted sweepers weren't fully addressed with my team. Sand-Drill is a non-issue as far as boosted sweepers go as Rotom can live a +2 Adamant LO Rock Slide and +4 w/o Rocks
Sand isn't much of a concern that point, and every other sweeper bar perhaps Zard X (and even that requires a +2 in speed to threaten me) can be handled by either Rotom or Meatfat.
On the topic of Metagross, one of the most important reasons why I use Gross over Tran is because Gross is a blanket check for both Fairies and special attackers while also providing one of Zard Y's biggest necessities to function: pursuit trapping. The Lati twins in particular wall most, if all, variations of Zard Y. With MLatias being a particular threat to the team in general, having a pursuit trapper that not only walls Latios, traps and bypasses Reflect Type MLatias, cripples Starmie as a spinner, blanket checks Keldeo, Clefable, MGard and lolMalt, while providing good synergy with Zard Y gives me so much freedom with my team building.
Perhaps my only concession is Lando, because to be quite frank Offensive Lando rarely has time to succeed. Defensive Lando or SpDef Tran are adequate replacements. That way I can have better insurance vs bird spam and MGross as previously mentioned. Or, if I go the Rocks Tar and Drill route, I could opt for scarf Lando.
In conclusion, I'll experiment with what I can do with the Lando spot. Ultimately this comes down to whether or not I can deal with Fairy/Bird spam better with my current team. That said I can always opt to switch Zard Y with Volcanion, but I have so many teams with Volcanion as it is that I honestly don't have the motivation to use it on this team.