Theoretical question on market cap

Hey monkeys, good day to all,

So here's the question:

Assume I have company A which is a holdco and owns say 50% of Company B and 50% of Company C and some other businesses. Companies A, B and C are all listed. Also assume that the industries these companies are in are safe, think utilities etc.

Am I correct to say that if company A is healthy and operating in a normalised manner (meaning no extreme debt or whatever pessimism), the market cap of A is likely to always be greater than that of the sum of 50% market cap of B and 50% market cap of C?

However, I have observed that this is frequently not the case, anyone has any insights on this? Some reasons I can think of could be the holdco is less liquid and hence investor value it at a discount, or perhaps its lack of a controlling stake in Companies B and C could also be a reason for the discount. Let me know your views or if you think I am incorrect.

Thanks fellas, appreciate the input!

Cheers, and happy Friday!