Everyone will have their own answer to this question but I took an X-T4, X1D, and IQ4 150A/Alpa STC (and iPhone) on my last adventure and they all make excellent travel cams in their own right.
It amazes me how powerful the STC/IQ4/70HR package is in such a small footprint. I’m going to make some 36x48” prints soon from the IQ4 shots and am pretty excited about it. The X1D and 35-75 is also a great travel package, and I’d be fine traveling with just it. The Fuji X is also great! I enjoyed the H4D/35-90mm I traveled with at one point but prefer all three of these systems over the H4D today, in part because they’re less bulky (the H OVF was glorious though).
the iPhone is great for what it is and everything it does, and I love the 10s of thousands of family pics I’ve taken with mine, but it’s not going to replace a “real” travel camera for me any time soon (Leica Q3 is next on my potential travel cam list to check out). I wouldn’t be nearly as excited about the prints if they were “iPhone only”. In 20 years, who knows where we’ll be but I’m loving the systems of today.