I would talk about how there are many things which can be done to improve performance. The first thing is always to investigate if the correct indexes are in place. Of particular concern in a normalized database is making sure FKs are indexed. Likely this would fix many performance issues.
Other things to look at would be rewriting the SQL code to use more performant techniques such as getting rid of cursors and correlated subqueries and making where clauses sargable. You would want to review the worst performing queries individually. You would also want to review queries that are frequently run (especially if multiple users run them simultaneously) as a small change in those could multiply through the system. If your worst queries are coming from an ORM, they might need to be rewritten as stored procs so they can be performance tuned.
You might also want to make sure you have a performance problem. What you might have is really a blocking problem where performant code is being blocked by other processes and has to wait.
Then you would look at hardware, if you have underpowered hardware and network connections, likely no other change is going to fix that.
In a large enterprise system, you might consider data partitioning.
Denormalization is a technique to improve performance but it is the last thing you would want to consider. First, you have the risk to the data of changing the structure that drastically. Converting the data to the new structure is something that can go very badly wrong if a mistake is made and it is more time-consuming to make this type of structural change than any of the other possible performance improvements. It would also be irresponsible to denormalize without creating triggers to make sure the data stays in synch as it is changed in the denormalized tables. This may mean selects are imporved but action queries are slower, so performance may not be imporved as much as you think. It is also a concern that in denormalizing, you may be making the tables significantly wider and that can affect performance negatively if you have wide tables.