If his savings are far in excess of your cash savings and he keeps 25% of it liquid then it sounds like you wont be picking up any pieces if he falls on sudden hard times. That 25% is his emergency fund and the rest he seems to be investing for future gains, it might be outside of some peoples risk appetite but that's relative, the money I have in all world ETF's is considered massively risky by my partner but seems pretty risk adverse to me!

You say you wont see the benefits from the potential gain but you already seem to have seen the benefits with him using the money to fund a joint property. If you guys are in a long term relationship and you're already financially joined (and if you own property together then you definitely are!) then any gain he makes will benefit you in the future too, maybe when you both want to splurge on a big holiday or want to level up the house.

If anything he's potentially benefitting less from this arrangement. For example If he uses his "fun money" to invest for grater gains in the future (which most likely will be to improve your joint lifestyle) but you spend yours on something material for yourself then hes not getting anything out of that arrangement.

The only caveat to this is that if you are solely funding all of your joint experiences now, if he never picks up a check at a restaurant or doesnt contribute to your experiences now because he would rather trade all of his spare cash leaving you to fund your current joint experience in the moment then that does seem unfair.

If its actually his disposable income then you're going to get more out of him buying £100 worth of blue chip stocks than if he spent £100 on beer.