For me, belts and bots both lose out to trains for the majority of the work.

All my factories end up decentralized with each node producing one or very rarely two outputs, and consuming only what they need. Trains transport everything between nodes, with one or more train per product type, with stations enabling or disabling automatically based on input starvation or output backlogging. But importantly, nothing besides 2x4 or 4x8 trains keeps up with the throughput without having stupid huge numbers of logistics bots. So trains end up being the majority of the transit.

Within a node it's majority belts, but bots for super high throughput short distances, especially in earlier nodes where I'm trying to saturate stupid quantities of e.g. iron, copper, or green circuit production. But each node doesn't have that much distance to cover, so there aren't that many belts relative to trains.

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Construction bots though, obviously first priority. All my nodes get built by a special construction train that drops off supplies to a temporary construction stop, and then robots do all of the constructing of a node.

I've seen "train only" bases, where carefully crafted Rail -> stack-inserter -> assembly machine mazes are built in such a way that still retains 8x Beacons per assesmbly machine.

But its very weird and obscure. With such a lacking in space, you have to run multiple train types and overlap them: either having mixed trains. And there's also the issue of "leftover" pieces staying on a stack inserter (ex: Stack inserter grabs 7 items, but then the assembly machine only accepts 3 of them, so now the inserter is "deadlocked" with 4 items. But the assembly machine needs another item, so everything deadlocks and shuts down).

There's ways to fix all these problems of course.

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But the easiest way is to instead use bots and/or belts to unload into the "last mile" going into the assembly machines. (Belt/bots can also reach 12 beacons per assembly machine if you're willing to have a faster, but more costly, design. Mainly for UPS wars rather than in-game benefits.)

But yeah, Trains are obviously the best bulk transfer item in the game. And while they aren't "unsuitable" for last-leg delivery per-assembly machine, its highly complex to do so. So its just easier to use belts/bots for that unless you're going crazy with UPS or something.

Yup agree completely. Train only with literally zero belts or bots is insanity. A small number (relatively) of belts or bots for feeding and internally within each node saves so much pain.

It would be like doing large data processing using exclusively map reduces with no non-MR orchestration at all. Yes you can technically do it, but, like, .... whyyyy.