I agree with you on all points, however, I have to commit to the technical infrastructure of the client.....
Indeed, I lose some of Seam's cool features. But I still have the Wizards in JBoss Tools and Eclipse, I don't need Spring and I lose a lot of XML maintainance, which still gives me a lot of production enhancements.
No problem, I just wanted to make sure you were aware of these things. It would be interesting to know what your client thinks the advantages are of their decision ;)