Do Italian trains tend to run "on time"?

The bus at Arona is a train replacement bus. It is there to receive passengers arriving on that particular train and continuing on to Stresa, around the track closure. It will not leave until all the passengers have made the transfer. If the train is late, it will wait for the train.

Oh good. I don't want to be hung out to dry in Arona!

And to answer your question generally, most of the trains have been running on time. I rode nine in May, and almost all of them arrived at the expected time.

Be sure your ticket is validated for either train or bus rides! You can do it through the Trenitalia app, or at the station if you have a physical ticket that doesn’t have an assigned seat.

Have a wonderful time!

I looked at the schedule. The 16:25 train plus bus combo will get you to Domodossola earlier than the 17:00 bus, but it is not faster—-the combo actually takes 10 minutes longer (2h30 min) than the bus (2h 20 minutes). Unless you need to be in Domodossola earlier, the direct bus seems a simpler option—-you board only once, and don’t have to worry about the train being late arriving at Arona.