There’s little actual weight difference in the frame between Bronson and Solo. The forks etc being smaller so the Solo is lighter.
I have a Bronson and my old 2010 714 Zesty, both 1 x 11. I still ride both, the Bronson is faster overall. Both are mediums but the Zesty is the same size as a large Bronson. I like the smaller frame on the Bronson its simply more manoeuvrable and the suspension is better. 650 tyres provide more grip patch contact with the ground which I like for technical climbs.
When I went out to replace the Zesty I developed the wish list from my Zesty geometry which I liked. I discounted bikes that were massively outside the geometry. My heart was set on a new Zesty which I demoed. Then I got a demo on the Bronson. I knew it was the bike for me.
If someone beats you up a hill – its because their fitness is better than yours (given the bikes are roughly the same weight).
Also its not all about the speed up. Alomg and down is just as important, which bike overall did you like best? Choose that one.