How can you not mention egypt's own royal tombs, which were chock full of rich artwork (somewhat we know because several KVs still have lot of artwork) e.g. https://en.wikipedia.org/wiki/File:Egypt.KV62.01.jpg in KV62, which is considered "modest wall decorations", or https://en.wikipedia.org/wiki/File:Egypt.KV43.01.jpg from KV43.