I like the Life deck, but I prefer it to be oriented around "Life Pay" rather than "Life Gain-Matters". Add another land or something that might make a deck list.
So if you are struggling to find a 3rd Orzhov card, just skip it. Basically cards that get passed and never make decks. Some color pairs have shit for good options anyway and if you try and force a specific number of gold cards or make each one super meaningful for a theme you want conveyed, you just wind up with suboptimal cube cards a lot of times. Being heavy handed with guild slots can send the wrong message about how deep (or shallow) a cube is but it's honestly not going to ruin your meta in most cases. I agree with the general sentiment though - you want flexibility probably more than narrowness, colors should stand on their own and interact in multiple ways and not be heavily dependent on your guild cards to tie them together. There is probably a sweet spot in the middle of all this but it's difficult to find without a lot of testing.
Go really low power and everything sucks unless you stack tons of synergy, but that's just a low power version of railway archetypal cubing masquerading as something more than it is. Not enough though, and it's all just good stuff and drafting is a bit shallow (just grab stuff that fits your curve and you have mana to cast - bam). Too much archetypal support and you get railway drafts as you point out. It's sort of a sliding scale though and honestly you'll have a hard time finding a perfect balance.