There is no reason to think such cost decline will apply to fusion reactors. Many of the parts in the system are mature (like, all the non nuclear parts like turbines.)
I'm hopeful that the research might bear fruit at some point, so I am glad to see it continue. We definitely shouldn't put all eggs in one basket, though.
We don't have a finished design yet, so who knows what parts are needed (yeah, a turbine is a given, but still...)?
Hope is not a plan, especially when that hope has proved illusory so many times in the past.