I know ez work like this but a good optimization can be done here.
Enabled sql debug and redirect
Create a new account:

1) the system will create a node : 7 query
1 insert
2 select
4 update
The same job can be done with 1 insert and 1 update
same pb with ezcontentobject_version/ezcontentobject etc etc

2) querys are repeat several time
SELECT contentobject_id, login, email, password_hash, password_hash_type
FROM ezuser
WHERE contentobject_id='new user id'

SELECT * FROM ezuser WHERE contentobject_id='11089' AND LENGTH( login ) > 0

3)another pb with ezcontentobject_link, the system will execute 3 query:
this query return 0 result
SELECT to_contentobject_id, relation_type FROM ezcontentobject_link
WHERE contentclassattribute_id='0'
AND from_contentobject_id='11089'
AND from_contentobject_version='1'
AND op_code='0'

this query is the "same" I know it won't return any result the systeml should not run it.

SELECT to_contentobject_id, op_code, relation_type FROM ezcontentobject_link
WHERE contentclassattribute_id='0'
AND from_contentobject_id='11089'
AND from_contentobject_version='1'
AND op_code!='0'
ORDER BY id ASC

We don't need to do this one because first query didn't return any result

DELETE FROM ezcontentobject_link
WHERE contentclassattribute_id='0'
AND from_contentobject_id='11089'
AND from_contentobject_version='1'