Note: I am assuming that it is 2027-28 and reliable AI automated coders exist (or the equivalent workhorse AI in your field), which makes implementation time negligible compared to making decisions. The effect is somewhat weaker with present-day-level AIs. I'm also assuming that the 100-person company is very competent with AI outside of making decisions, but that the startup can plan things much faster due to not needing a committee to do so.
Very rough maths:
If your 100 person team still follows collaborative processes to cancel out errors (let's say it takes 10 people a day to decide on a single deliverable's shape), then give the design to the AI to implement (as we assume the AI can do it without supervision), then you can ship 10 deliverables a day.
At the same time, that 4 people team can have all of them bouncing ideas off of AIs to help them make decisions in rapidfire all day. They'll each individually spend an hour working on a decision then hand it to an AI. Their decisions are on average as good as your 10-member team meetings because while your medium-sized company's decisions sometimes end up suboptimal due to politics, the startup's decisions are individuals so make the wrong call more often, and I assume these two effects cancel out. In that case, your competitor with 4 people cranks out 32 deliverables a day assuming that the implementation AIs don't have to be supervised at all.
In summary it's not "move fast and break things", it's just "move fast, focus on making decisions, delegate everything else to the AI". Remember that the decisions are all that matters if the AI can do all the implementation.
