Totally agree. As someone who recently came across Steemit, it was definitely confusing at first. I think the idea behind the SBD was to (originally) give people confidence that their post had tangible and meaningful value. So, when STEEM was less than a dollar, what it displayed onscreen shouldn't have needed converting, and you could feel confident that X post was earning 20 or 30 dollars. But as you say, now it doesn't really work.
If we change it to only be liquid STEEM and SP (still think it's simple enough to understand the difference there), there's still a conversion problem if you want to understand fiat value. But maybe if a platform like Steemit or Busy were to build in a currency converter function, that you could toggle on/off, it could display STEEM you are receiving, and then do live conversions to whatever your default fiat is if you select it.
One thing I think needs a change is in the 50/50 split vs 100% SP. From a game theory/incentive standpoint, SP is more valuable to the network as a whole than is liquid steem, because it's not immediately tradeable. Having "stake" is seen as a good thing. As such, there should be incentive, if you don't need to sell immediately, to do 100% OVER 50/50. Maybe you get more Author rewards, or the platform takes less beneficiary cut (say 10% vs 25%) of your post rewards if you choose to essentially reinvest 100% of the earnings into the system on payout.