There is ongoing research into decoy selection: https://ccs.getmonero.org/proposals/Rucknium-OSPEAD-Fortifying-Monero-Against-Statistical-Attack.html Also in the next release, the ring size will be increased from 11 to 16.

You can also churn (send your funds to yourself) to increase plausible deniability (churn TXs look the same as regular TXs on-chain, and can create distance between the true sender and recipient).

Complicated cryptography is sometimes necessary for advanced features, such as strong on-chain privacy-by-default. Monero is open source and people are welcome to audit the code or improve it.