Some riders are just faster OOS, see Pantani for example. By "sections that required us to stay seated" do you mean on the flat or on loose gravel climbs?
You say that seated, lactate builds in your legs and your breathing gets too fast. Having both those things happen at the same time AND being faster OOS on the same terrain would be unusual. "Breathing gets too fast" usually means cadence is too high. "Lactate builds in your legs" usually means cadence is too low. OTOH, that latter might also mean better technique is needed as scottfsmith says. Gravel isn't the same as pavement in that there is more resistance to forward motion on the flat, which means that it's always more like climbing than hammering on the flat and smoother pedaling gets better results. Since you are as fast or faster OOS on climbs than seated riders, your aerobic capacity must be better and it must just be a matter of more appropriate seated technique.
Another thought is that of course you climb OOS at a lower cadence than is usual for you seated. You could try a lower cadence seated, combined with a more consistent application of force around the pedal circle. Not pulling up of course, but unweighting the up pedal, pushing forward at TDC, and pulling back at bottom and another 20°-30° after BDC. That should spread the effort out among more muscles while lowering oxygen cost at the same time.
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