This is in the context of the typical lane-based land teamgames, which is a great situation for snipers because of high available apm, reduced effectiveness of T1/T2, and smaller areas to cover so less unit speed required.
I think vs Aeon/Sera they ruin the entire land domain and turn it into a static t2 shield + mobile arty + sniper war because they beat every T3 land unit and Ythotha/GC.
Against Cybran they're overpowered and force Cybran to give up nearly everything and rush Megalith, although I'm still developing my playstyle as Cybran against snipers so that's not my final opinion. Mobile arty and static shields seem too weak and slow to build for Cybran, especially vs Seraphim. Firebeetles require a lot of precise sacrifices to get through to the snipers so idk if it's a possible solution to hold them off until Megalith finishes. Also when I play, after Mega finishes it usually just dies to GC or Ythotha + army/2nd T4 (bricks are so bad vs GC claw DPS/Ythotha splash now they cant help mega win and survive to snowball megas), so it's not even a proper solution. Monkeylord is simply bad against snipers.
Against UEF they're good and the only way to stop percies besides ACU/PD, but they don't scale nearly as much as vs Cybran because UEF has spearheads to keep the sniper count down and limit apm, ravagers to just kill snipers for 2k mass, and fatboy at 28k mass to make snipers unusable.
They're super vulnerable to air so it can happen that your entire army gets wiped in 1 air attack because of a smaller air loss compared to what is needed to wipe armies of other compositions. Usually this means you don't infinitely scale snipers and try to go T4s+othuum/harb just for the safety, even though snipers are better.
They're kinda optional to play in 1-1.8k teamgames because othuum/harb + shields can begin to kill ACUs and othuum/harb drops are easy to get through and they deal devastating damage. This is like a general trend of later game efficient choices being played rarer because people are too bad to keep the game even for that long.