Yeah, I don't agree at all. If you're talking Constructed where 4 CMC isn't efficient then sure, but I don't think it's applicable to most cubes. Venser is still one of the best blue creatures in cube given the flexibility of what you get at instant speed for 4 mana. The typical 3 CMC bounce creature effect at sorcery speed isn't as good as it once was, but I don't think it applies to him.
Venser's not generating value that leaves you with something extra like some of the designs we get nowadays, but its utility are what let it still find homes in powerful environments. Being able to bounce problem permanents off the field, set back development with a land bounce, or just do a
Remand impression on curve is still very strong gameplay. If you can use that ETB effect twice in a turn with a blink effect like
Soulherder or
Thassa, Deep-Dwelling it can be backbreaking. If there's nothing relevant you can just hold it back and leave your mana open, worst case it's a Flash 2/2 that bounced one of their lands on an empty boardstate and will then start attacking next turn.
Unless you're straight up trying to port Modern/Legacy over where 4 CMC is too much, Venser is still a good cube card. Its extremely flexible, has a vast number of potential interactions with other cube inclusions on a variety of power levels. It's strong but not busted, even 14 years later. It's no design mistake ala Uro or Oko which broke the game, but I don't think that makes it extremely weak.