I say, relax. A trip around the world is not a race. Otherwise, you can also speed bike if you want to do as many kilometers as possible. So I wouldn't invest too much in advance just because something might break. I also wouldn't worry too much about everything that could break. Then you can lug a spare bike along if you're so worried about something breaking. If something isn't available locally, it doesn't matter. There are always shared taxis or minibuses where you can get something sent to you. The two bikes can usually easily manage 100,000 km without breaking down. The bikes aren't mountain bikes. But do you want to ride mountain bike trails? Probably not. Then you take a mountain bike.
When I read a sentence like that, I get a crisis. But there are all different ones. I always want to be as light as possible on the road. The supposed safety of not having to push the bike up the hill in front of me, but rather riding it. You have to decide in advance what you want. If you want to ride on the road, you take tires that run smoothly. Off-road, you just need a bit of tread. Without a tread, you can do some gravel riding, no problem, but it's faster on the road. With tread, the road is slow and the hills are heavy, but off-road is better. So if you only ride on poor roads every now and then, for example to find a quiet place to sleep, then you should go for a light one. The outback is probably not on your doorstep. So there is the possibility of making changes to the setup. The world is largely globalized. That's why I think the question of which power converter do you have is much more important? Forum charger or power station, or... Someone else has already written, pack your bike full of the stuff you want to take with you, ride up a hill with it and think about what you can optimize. But to be honest, apart from the world trip, you haven't written much about what it should look like. With 3 pairs of underpants, a suit and 2 jerseys for driving around the northern hemisphere with a well-filled check card, or would you rather go with self-support with all the stuff including a chair and coffee machine through Papua New Guinea. But that wouldn't matter either, because everything can be shipped and delivered with UPS.