Seeds and Mana in the Spire have been manageable, and sentients haven't been required yet. We'll see how that goes....
Funny, but it's not the sentient goods that cause me to hybrid. I have 3 sentient goods factories for each tier, and they keep me supplied quite nicely for catering. I usually hybrid cater/fight when I run out of orcs (despite having tons of orc nests). I'm using too many orcs at the moment to feed my beer gardens.
I'm in chapter 16, and I do believe that, given the fact that I have 6 maxed planks, 4 maxed dust, 6 maxed silk, and the sentients, I could conceivably cater everything and still get to silver in spire every week and 4K or more every week in tourney. It is possible without spending diamonds.
I did about half/half catering and fighting this week, got to gold in the spire and made 8th place overall in tourney in Sinya. If I had catered only, I would have probably stopped at silver and gotten only 4K in tourney. But for a lot of people, that's good enough and they're happy with it. If so, then there's no reason they couldn't exclusively cater through chapter 16 at least.