εἶδος (G1491) emphasizes on the outward appearance.
μορφῇ (G3444) emphasizes on the inward structure.
Both means representational form but they are not synonyms. In fact, they have somewhat opposite meanings.
Classical Greek influenced NT Biblical Greek but they are not exactly the same language. Put a higher weight on the Biblical usages of these two words and less weight on the extra-Biblical writings.
The word form μορφῇ (morphé) is the Greek root for the words metamorphosis and morphing. It is unfortunate that the English word form emphasizes too much on the outward appearance. We are images of God. We are not morphés of God. The morphé of God is the form and content of God. The Godhead morphs into a representational form for our perception and interaction conveniences.