You are having the wrong idea in both cases then.
Lumia 535 got 540p(qHD) 5" IPS LCD which boils down to 220 ppi. It does not have any enhancements like CBD and is extremely poor in sunlight.
820 has 480p 4.3" Amoled display and has 217 PPI which is virtually identical to 535 since this AMOLED is not of the pentile variety.
Coming to processor. Its not about the amount of cores its about quality of the architecture they are based on.
Lumia 820 has 1.5 ghz Dual Core Krait which are based Cortex A9 architecture and a adreno 225 GPU.
The 535 is a cortex a7 stock core based 1.2 GHz quad core.
Each cortex A9 core delivers up to 50% more performance than a similarly clocked cortex a7 and adreno 225 is faster than even the 305 and thus is obviously a lot faster than 302 found in 535.
Higher amount of cores can surely help in multitasking but in the app opening and the general performance will always be better on higher architecture.