First Switzerland Trip

I think your itinerary is pretty good. If it were me, I'd take a day from Vevey and add to Wengen. Bern is nice, but I'd do it as a day trip from Luzern. On Lake Geneva, Chateau Chillion was enjoyable. We are "sciency" types and we found CERN outside Geneva interesting. In Luzern, we enjoyed the boat trip and cog wheel train up to Mt. Rigi. We spent a lot of time walking around Luzern. We were in BO in winter, but, we loved walking through Gimmelwald a few times, the walk from Murren into Gimmelwald, we enjoyed the trip up to Schilthorn. The Jungfrau was never clear. On Lake Como, we enjoyed walking around in Varenna and Bellagio. (The RS guide had some walking tours) I highly recommend Villa del Balbianello

https://community.ricksteves.com/travel-forum/trip-reports/lucerne-62eb4d28-60ab-4837-b4b4-91a2486eb732

https://community.ricksteves.com/travel-forum/trip-reports/venice-lake-como-sorrento-amalfi-coast-with-lots-of-rain

Above are my Trip Reports, hopefully you'll find some helpful info.
We just returned from Lake Como this past May, and I can't wait to return already.
I'd definitely recommend spending the night before the return flight in Milan. In our experience, the regional train from Varenna to Milan is usually SRO, but it's only an hour.
I hope you're considering riding the Bernini Express route from Switzerland into Tirano Italy. It is an incredibly beautiful route, and you can ride the regional trains, which have more schedule options than the panaoramic trains, and use the same tracks. From Tirano you can easily get to Varenna.
I like Bern, but it's not a priority, when you have all these other beautiful places to explore.
Have a great trip. Safe travels!

I would not add Bern. It's a nice city, but it's not in the mountains. I might shave a night from Varenna and stay in Milan the last night. But no bad decisions here.

4 nights in Luzern may be a bit much unless you do more than one mountain excursion. We currently are booked for 2 nights in Luzern with a TBL walking tour, concert at the KKL on arrival day and Mt. PIlatus on Day 2. Previously we did a walking tour there, noon concert at Jesuit Church, a one hour boat cruise and a day trip to Mt. Rigi when we stayed at Hotel Balm in Meggen. Our upcoming 4 nights in Wengen after Luzern is beginning to feel like too short a time there. Bern was fine for us as a day trip from Villars-sur-Ollon, where we spent a timeshare week and found plenty of day trips from there via rental car, so maybe one night in Bern will suffice?

Thank you all for your feedback! I am thinking of tweaking some more based on your comments!

Nice plan overall! I would shave a night from Luzern and add it to Wengen. 3 nights is also sufficient for Varenna, IMO. You might enjoy a last night in Milan if only to make certain you suffer no delays getting to your flight.