The TIE vs Death Star explosions - I'm OK with them as is because of the relative size differences.
A standard TIE fighter is listed as being about 6m (I'm guessing that's height). Now, relative to that, I'm going to guess that the explosion it created was somewhere on the order of 15m tall.
The Death Star is listed as being about 120km - literally 20,000 times larger than a TIE. That means the explosion it generates is somewhere on the order of 150km.
If you put the TIE explosion next to the DS explosion "in scale" the TIE looks like a tiny flash, no bigger than a flickering star, by comparison.
Relative to the sizes of the craft generating them, the explosion sizes are accurate. What's probably throwing you off is the visual aspect - the amount of screen space the explosions takes up, the perceived distance between viewer and explosions and the visual styles of the different explosion effects.