Gee is filled with Taengsic runs and adlibs after the bridge, which is more than can be said about most kpop songs now. Most snsd titles were like that and the Boys 100% isn't easy
Get the distinct feeling you've never heard of any of these groups and are just skimming google lmao
Runs and adlibs are not inherently vocally intense. Anyone can do adlibs and none of the runs in gee after the bridge are exactly pushing Taeyeon nor Jessica's limits. There mere existence doesn't mean they're particularly difficult to execute.
I've listened to ton of T-ara. I'kll admit to not caring much for The Seeya, (Can only name one track between both versions.) but c'mon T-ara is not a vocal powerhouse of a group and never been sold as such. You really gonna argue that Soyeon or Eunjung can outsing this generation?