Is a cast iron wok too heavy?

That will be extremely heavy! Very cumbersome.

Traditionally, woks are not cast iron, but steel. They get really hot really fast. They are easy to flip stuff around in as you stir fry. Get one with a flat bottom so that it has maximum contact with your heat source as our stoves don't get anywhere close to as hot as a traditional heat source for a round bottom wok.

America's Test Kitchen does a wonderful video on the subject!

Woks tend to be pressed steel rather than cast iron.

It's not just the weight it's the leverage. A good 36cm (14") steel wok on a single handle is not easy to lift when empty; when full tossing ingredients is mainly a case of tilting it by pushing down on the handle rather than throwing it around like a skillet… & bringing the plates to the pan to serve.
A two-handled wok is an easier lift, but you don't have a spare hand for serving.

My 36cm wok weighs 1.85kg (about 4 pounds) though it is of particularly thick steel, you can get lighter - I'm a 6ft bloke of reasonable fitness & find it possible but quite an effort to lift by the single handle when it's full. (I don't mean full to the top, I mean with a stir-fry & noodles in it.)

A late thought: The cast iron woks I've seen in use in restaurant situations (mainly in Japan, I've never been elsewhere in South-East Asia) have tended to be as deep-fryers, for such as tempura, so no lifting or throwing required,

I own a 40cm (16") cast iron wok and love it. But it is a different kind of pan from a steel plate wok.
And it is heavy, very heavy.

If you want a wok, steel plate as it is used in Asia. But if you want a versatile pan in wok shape, cast iron can work well.