First of all, if you think many of the 5e rules are poorly thought out, you aren't jaded, you just have learned the rules well enough to see the flaws.
Second, the chart showing all 0s is incomplete. You only look at Paladin/Ranger and EK/AT multiclasses. Rounding up is fine for those specific homogeneous combinations, but there are other combinations where you end up with a +1 by rounding up. At some point someone looked at the chart and realized that a Paladin 1/Cleric 7 has the same spell slots as a Cleric 8 and thought it was bad because paladins are supposed to have less spellcasting than clerics. And same thing with Ranger 1/Druid 7 matching a Druid 8, and probably some clever combination like EK 5/Wizard 5 matching a Wizard 7. So, because of these specific edge cases, we all get stuck rounding down.
That's because they're the only ones with a direct compariso.
Also what's wrong with those edge cases (excepting that half casters don't count at level 1)?
So the EK 5/Wizard 5 counts as a Wizard 7, what's wrong with that? An EK 5 by itself has the slots of a Wizard 2. Why should it lose out?
A Ranger 3 has the slots of a Druid 2, so why's a Ranger 3/Druid 7 having the slots of a Druid 9 a problem?