p.3 #1 · do i REALLY need to take the 16-35/4 for landscapes?
Your milage may vary, but I have never taken anything wider than a lowly EF 24mm f/2.8 to Asia. It did just fine. There's always stitching if you really need to go wide. I'm not saying it's a great lens, but it fits easily in a jacket pocket or even cargo pants if need be. The 24mm pancake would be even better.
p.3 #3 · do i REALLY need to take the 16-35/4 for landscapes?
I have yet to read all the responses to this thread but I've been to parts of SEA multiple times over the years. I'm also a lover of wide angle shots. I'd say bring something wider than a 24mm.
Not sure of your specific locations in these cities but Old Town in Hanoi is a bit tight and congested, especially Train Street, so having a wide angle helps at times.
Do you "need" wider than 24mm? No. But it's a nice to have. Personally, on vacations, I also like to travel light (no checked bag). My lens choices are usually a wide angle and something telephoto. I rarely bring anything in the standard zoom range.
p.3 #4 · do i REALLY need to take the 16-35/4 for landscapes?
My most recent combo for these types of adventures has been the Canon R10 + tiny RFS 10-18 + RFS 18-150. Incredibly light and compact. For some trips I’ll throw in the compact RF 100-400. These clearly are not fast lenses, but for size/weight and FL coverage while traveling, this APS-C kit has been a worthwhile trade. If I need a faster lens, I can toss in the 35-1.8 or 50-1.8. Both are small/light. A not-much-bigger full-frame configuration would be the R8(or your R) with 16-2.8 and RF 24-105 STM. My iPhone is my backup when traveling like this. Your trip will be awesome. Have fun!
p.3 #5 · do i REALLY need to take the 16-35/4 for landscapes?
Last month I was on a two week trip to Spain. My RF 24-240mm worked well, but my RF 16-28mm f2.8 showed way too much distortion at 16mm on my R6II. If I could re-do that trip, I would probably just take my R6II with my RF 24-240mm f4-6.3 and my RF 16mm f2.8 STM. That's if I wanted to take my Canon gear.
However, like you, I also use two other systems (Sony and Micro Four Thirds). If I want to travel super light and not worry about drawing attention to myself or worry about my gear getting stolen or rained on, I take my OM-5 with 3 lenses (Panasonic/Leica 9mm f1.7, Panasonic 12-35mm f2.8 and OM System 45-150mm f4 Pro). My m4/3 system fits into a tiny sling bag and weighs next to nothing.
