Compared to the likes of Ethereum, Bitcoin is super simple. Compared to others, it's still somewhat complicated.
While the use of PoW for consensus is super simple (most cumulative difficulty wins), Bitcoin script is a huge source of complexity in itself, with tons of warts. As it turns out, you don't need script to do payments, multi-signatures, atomic swaps, discreet log contracts, bidirectional payment channels etc., i.e. nearly all of the functionality that script is used for. All those can be done with so-called script-less scripts [1], which is mostly creative use of Schnorr signatures.
Bitcoin's emission is not that simple either with the reward halvings every 4 years. A fixed block subsidy (i.e. pure linear emission) is not only simpler, but arguably fairer too, avoiding a concentration of wealth on early miners/adopters, and leaving later generations more than mere crumbs.
[1] https://suredbits.com/schnorr-applications-scriptless-script...