If you simply added the spell slots of the two classes you would end up poorer. ESL 3 grants 4 level 1 slots and 2 level 2 slots. Simply adding the slots from lvl 2 paladin and lvl 4 EK gives you 5 level 1 slots and no level 2 slots.
You are complaining about having only 4 lvl 1 slots without acknowledging the level 2 slots that you would not have access to under your scheme.
The Larian/DnD 5e scheme is unambiguously better than your proposal.
