The Snake Draft tournament is currently ending and Mega Latias has been available in the tier throughout the tour. I've noticed that the discussions didnt make much use of high level replays even though 45 extremely competitive games occured while Mega Latias was available in the tier. Weavile and Mega Gardevoir were also available back then so I won't use replays in which those 2 had a significant impact.
http://replay.pokemonshowdown.com/smogtours-gen7uu-314766: Latias weakens significantly Mantine but gets poisoned in the process. It also managed to cripple Coba with Thunder-Wave which was quite good for me, however this replay also shows that Latias is quite weak without any spA, it failed to 2hko Cobalion and it could have been used as a set up fodder by a potential sub cm raikou.
http://replay.pokemonshowdown.com/smogtours-gen7uu-315477: Lycan's Mega Latias dodges a Thunder-Wave from Rotom-W but still fails to do anything significant. It had Dragon Pulse and HP Fire which was one of the best potential variants to beat my team but it still needed to predict on some key turns and to get a bit lucky to have an impact.
http://replay.pokemonshowdown.com/smogtours-gen7uu-317092: Latias faces stall and gets walled by Doublade and Blissey throughout the game thus failing to do anything.
http://replay.pokemonshowdown.com/smogtours-gen7uu-317245: Tesung's Latias does quite well here, HP Fire + Defog helped him a lot vs Klefki and it also got a kill on Hydreigon thanks to a good prediction. This shows the potential of supports sets which I find good but still far from groundbreaking.
http://replay.pokemonshowdown.com/smogtours-gen7uu-314913: Thanks to Weavile and Scizor's support, Latias ends up cleaning HT's weakened team. This shows how goold volt turn cores are at supporting fast win conditions but it also means that Latias can't just win on its own as some people seem to claim.
http://replay.pokemonshowdown.com/smogtours-gen7uu-317209: McM's latias gets trapped by a surprise Pursuit Snorlax and does nothing the whole game. This is a good exemple of an effective Latias lure.
http://replay.pokemonshowdown.com/smogtours-gen7uu-321351: Pearl's Offensive Latias manages to take down a Blissey at the cost of most of it's health thus letting tesung's Aero trapkill it. This shows that Latias can do well vs stall with the right variant but it is yet again far from being able to break them on its own.
http://replay.pokemonshowdown.com/smogtours-gen7ou-325482: Analytics Latias is sacrificed early on, most likely because it didn't have any tools to break Stall.
http://replay.pokemonshowdown.com/smogtours-gen7ou-324903: Lycans Latias puts in some work here, it walled Nihilego throughout the game and also forced Gliscor out a few times, it was still walled by Mcm's umbreon throughout the game though. McM's Latias on the other end, turned out to be walled by Mantine thus making it unable to do much this game.
These games show that Latias is usually better on paper than in practice. It is indeed able to fill many roles on team but each set has its flaws and require proper support to work decently. It's also true that finding out which variant is being used can be frustrating but the fact that Latias isnt that powerful makes it easier to scout its set so as to beat it properly. It takes some slight preparation to beat Latias but all things considered I don't think is nearly as threatening as many people seem to think.