It all depends on the current block reward for the Magi network. The more hashrate there is on the network, the lower the reward will be. As such, you will need to use the least cores possible, as adding more cores will greatly reduce the reward you're going to get. Magi works this way to prevent big miners with high-end equipment to take advantage of the rewards. Therefore, if all people mining on the XMG network would use the least amount of hashrate possible, then rewards will be better. You're going to need to check regularly the network's stats to see current block reward and mine some XMG with 1 to 2 cores only. I've done this and it has worked so far.
Yeah. Mining with a CPU is not as good as it used to be in the early days of cryptocurrencies. With a GPU, you could get better results, but not everyone has access to high-end GPUs. As such, I believe that CPU mining is more accessible as it allows nearly anyone to get started in the mining process. This model makes it much more decentralized as everyone can participate in the process (unlike GPUs and ASICs).
Nevertheless, while CPU mining is not profitable anymore, it is still a fun process to do with your PC. My most favorite CPU mineable coins are HODL and XMG as they provide the ability to easily mine a few coins with them, and multiply your earnings by just holding your balances into your wallet.