Technically, it is possible to decrease the size further.
However, there are diminishing returns, pros and cons of futher pruning (currently, a pruned node can still serve some of the blockchain, by design), pros and cons of ease and speed of accessing data (some data is kept duplicated in the database for lookup purposes), etc.
You bring a comparison with Bitcoin, and one important point of difference between the two is that Monero's RingCT outputs are pretty much never known spent, so you can't drop these ever, whereas Bitcoin can.