Currently, the argument for scarcity looks good with EIP1559 where the gas fee will consist of a burned base fee and a tip to the miner resulting in overall lower fees causing a potentially deflationary supply. But Ethereum's scarcity is to a larger extends a moving target than say Bitcoin or Monero.
The other reasons for investing OP mentioned were enough for me to go deep a year ago: cash flow, network effects and developer tooling/adoption like no other L1 chain. I looked at other smart contract chain's developer resources for dapp dev and no other's come close to Ethereum. I have been learning Solidity dapp development in my free time since and can recommend the experience.
I don't think scarcity is a realistic point in the investment thesis.