he seems really sensible! I probably save a similar percentage of my salary and have slightly more saved. I don't think it's extreme! I'm saving both for things I want and for the future, e.g. pay my mortgage off so I'm not giving the bank tens of thousands in interest and can retire earlier rather than working until I'm 75! If there is something I want then I buy it, but I don't buy stuff just for the sake of it.
He already spends £2300 a month, and I'm assuming given you live together and split all bills that only a bit of that is on necessary expenditure, so it's not like he's only paying for basic living expenses and saving everything else - he's covering himself and spending a fair amount on luxuries (if you consider all non-essential spending as luxuries) - who are you to tell him he should be spending even more?
It would be different if he never treated you at all, but people don't all consider the same things to be worth spending money on. Some people consider nice hotels etc a complete waste, therefore why would he spend his money on something expensive that isn't a treat for him?
If you want to negotiate doing something together as a treat, fair enough, but it should be a) something you both want to do, and b) a shared expense
Otherwise it's like him telling you that you should spend your money on football season tickets/expensive cycling or fishing gear/front row tickets to heavy metal gigs (just trying to think of examples of things that would be up to personal taste as to whether they were 'worth' spending money on or not).
You both cover the bills, then you spend your remaining money on what you want, he spends his on what he wants. He's got no obligation to spend a significant amount of his money on you (rather than doing what he wants with it, whether that's saving it or spending it on something you don't think is worth it) just because you're dating! and of course also vice-versa.