how to sucessfully revoke view any definition (or any other server permissions)?
I believe this is because when you ran:

GRANT VIEW ANY DEFINITION TO [mycompany\webDevSeniors]
GO


Grant was given to that particular user. But when you tried to revoke, that was at the schema level.(2nd run). However when initially you gave the GRANT access , it was not specified at object level.Since REVOKE has no affect if the specified permission does not already exist.

I believe starting with creation of user and then assigning the roles accordingly can help here.

Please read Understanding GRANT, DENY, and REVOKE in SQL Server which will help you in this scenario.