In middle egyptian (the language you probably assume) "pictures" are just syllables. They are phonetic, not semantic, in the same way letter of modern language correspond to sounds, not meanings.
Egyptians had no problem expressinyg conplex concepts and they also had cursive writing, which is much easier to write.
The phonetic symbols included in the Egyptian writing system represented 1 consonant or 2 consonants or 3 consonants, not syllables. Any syllables or short syllable sequences with the same consonants were written with the same symbol.
This makes the Egyptian writing system an exception, as all other writing systems that have developed completely independently, instead of being inspired by an existing system, have used phonetic symbols for syllables.
This is the very reason why the Egyptian writing system has generated the ancient Semitic alphabet with 29 consonannts, from which all later Semitic consonantic alphabets have been derived, then the Greek alphabet and other European alphabets, and the Indian writing systems and other Asian writing systems derived from them.
Since the beginning, the Egyptian writing system had two variants, depending on the writing instruments: hieroglyphic for inscriptions carved in stone and hieratic for texts written with a reed brush on papyrus. The latter is what you mean by "cursive". "Cursive" is not really appropriate, as hieratic was still a very complex script, difficult to write, even if it was simplified in comparison with hieroglyphic. Millennia later, a more cursive form of hieratic developed into the demotic script.
The point stands still: the writing was not as clean as modern alphabets but was capable of expressing abstract concepts, it is completly orthogonal to concepts expressed in writing.
Some proto-writing systems (e.g. Australian message sticks), which could not express all ideas, were just very simple dots and lines. Going from being able to express only certain things to the full spoken language and going from complex symbols to simple ones which are easy to write are two different processes. So while we can suspect that a pictoral system is from an early stage of a writing system we cannot say that it is necessarily primitive in ability to express all ideas. Plus it might be, like hieroglyphs, only used for fancy texts for monuments and similar.
I'd wager the Great Pyramids will still be around in 1000 years and the Burj Khalifa will not, if anyone wants to take bets.
The closest analogy might be: modern alebraic notation is compact and clean but this doesnt mean algebra didnt exist much, much earlier.
