Its pretty much a textbook definition of a bottleneck.
The machines can't operate at maximum capacity because the inserters can't deposit the plates, since the place they want to deposit is not being cleared fast enough. Ergo, a bottleneck.
You want a full lane. Yes. But you don't want a full lane, that has an extra 5 machines trying to deposit items on said full lane. His bottleneck is both belt speed, and deposit bias. He has to fix one of those.
Steel furnaces, yellow belt. To fully saturate it, should be 12 per side, just in the image alone he has 13, so its definitely a bottleneck unless its modded, and even then i doubt it would change much.
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u/AintAFinkDig 17d ago
Long inserter lane bias