You could tactfully let him know that financial/regulatory landscape for ETH isn’t yet certain in terms of security/commodity. This will add additional unknown risk factors to the price volatility risk he is already exposed to. 

If his goal to hold them is for the long term (the best play to balance out short term price volatility) then maybe he should consider Bitcoin as the safe hedge against an uncertain backdrop. Likely he is still very exposed to uncertainty of the fiat system and ETH just is a proxy for that rather than hedge against.

Also send him a good nostr:npub15dqlghlewk84wz3pkqqvzl2w2w36f97g89ljds8x6c094nlu02vqjllm5m video or two that you think he will watch. Being a business owner he may well appreciate the logic behind MSTR holding BTC on their balance sheet outside of operating costs.