There was a poll here a few months ago that, IIRC, showed the overwhelming majority of respondents were solo tourists. I'm one of them. That supports the thesis that touring is essentially a solo endeavor.
The best partnerships I've seen and had were made on the road.
Those who start out sharing gear and trying to adapt to each others' styles often have a tough time. Though, as in marriage, nothing worthwhile is ever easy, is it? Those teams can grow emotionally and get very close and that's something to strive for. I met Rowan and Machka last year and they're a great example.