This is a great topic. I have been working on TAO for many years. I am not very familiar with other graph databases; I assume fundamentally they are more or less the same. Here are some differences between RDB and a graph db IMHO,
1. sharding and transaction boundary
2. Secondary index support
3. How “join” works (eg. give me a list of my friends who follows Justin Bieber)
You’re right that graph db is very easy to use a lot of the times.
It does, which one can argue it’s an implementation detail. The differences I mentioned above eg sharding, transaction boundary, secondary indices, etc. should be generally applicable to a non-relational db and not unique to TAO. I could be wrong though; as I know little about other graph dbs.
It would probably be more productive to compare RDB and Graph with certain workload examples (OLTP, OLAP, joins, scans, etc.).
You’re right that graph db is very easy to use a lot of the times.