Garmin Instinct 3 AMOLED 50 vs Amazfit T-Rex 3 Pro. Which would you choose for long-term adventure use?

I'm trying to decide between the Garmin Instinct 3 AMOLED 50mm and Amazfit T-Rex 3 Pro 48mm, and I'd really appreciate input from people who have actually used either watch for a while.

I'm not a serious athlete. My primary use would be:

• Long motorcycle rides and some off-road/trail riding
• Occasional Hiking and trekking
• Future high-altitude treks which include some 10-day treks (I always carry a Power bank)
• GPS/navigation and route tracking
• General fitness, sleep, HR, SpO₂, VO₂ Max, altitude, etc.
• Strava integration
• Regular exposure to rain, dust, sweat and rough outdoor conditions

I'm looking for something I can comfortably use for at least 5 years, rather than upgrading every couple of years. Expecting 10 days of battery life with 1hr of Walking or Cycling activity every day. I am upgrading from Samsung Fit 3 currently.

On paper, the T-Rex 3 Pro is extremely attractive: sapphire glass, titanium bezel, offline maps, dual-band GPS, long battery life, flashlight, 10 ATM, etc. The Instinct 3 has the stronger reputation for long-term reliability, Garmin's more mature ecosystem and training/recovery data.

My biggest questions are:

1. How does T-Rex 3 Pro hold up after 2-4+ years of real-world use?
2. How reliable are GPS, altitude/barometer and HR data compared with Garmin?
3. For hiking/high-altitude trekking, how good is the offline mapping/navigation in practice?
4. Has anyone had battery, AMOLED, button or charging failures?
5. For people who have owned both Garmin and Amazfit, does Garmin's software/ecosystem actually make a meaningful difference for a serious non-athlete?
6. How has Amazfit's software and Zepp app experience been over the long term?
7. Most importantly, if the two were closely priced, which one would you personally buy and why?
8. I see horrible after sales and support experience in India for Amazfit. So, I am little skeptical on this. The watch is very promising, but after the initial 1-year warranty period, I am left helpless with no part/service support.

I'm particularly interested in long-term owner experiences rather than launch reviews/spec-sheet comparisons.

Thanks! Would love to hear both positive and negative experiences.
r/Garmininstinct r/amazfit r/Garmin