I think nerfing bots would make me use also higher tiers of belts, but it would make many players angry. Nerfing bots could be a setting for the game similar to research cost.
At the same time I think there are many ways to make belts more attractive:
- Make an infinite research technology that speeds up belts - you have this for mining efficiency, for bot speed, why not for belt speed? (side note: and why not for general assembly machine speed?)
- Make belts easier to use with inserters: give inserters the option to insert not always on the "right far end" of their target field, but also "left near" or "right near" or "left far" end of the target field. This would be a transparent change for existing saves and give new possibilities to use inserters with belts. It would remove the need to construct the same standard patterns for inserting items to near ends of belts over and over again (these patterns are cool, yes, but they require an unreasonable amount of space). I would call this change "un-nerfing inserter/belt usage patterns". There can be an achievement for not using this feature.
- Make belts with the same item on both lanes easier to balance, by creating a "balancer" belt field that feeds whatever comes in on both lanes to both output lanes in the same ratio. It is possible to build this with two splitters and a few belts but (like above) it takes a lot of space and looks unintuitive. This I would call un-nerfing single belt balancing. (It might open a whole new set of patterns for multi-belt balancing.)
- Make it an intended feature to make designs where belts contain two item on one lane in a certain ratio. This allows to have one belt delivering four types of items to a factory. Why is this fair compared to bots? Because requester chests can deliver more than four (eight, or is it sixteen?) independent items to a factory, in a free ratio, including optional buffering ability (very powerful! maybe this could be nerfed in some way, by reducing the number of item types that can be requested at the same time to 2?).
Possibilities to facilitate belts with more than two items on one lane:
- Make a "synchronized stack filter inserter" that takes for each input filter one item, waits until all input filters have received one item, and then delivers the items in the order of input filters to the belt. The number of input filters could be 2 in the beginning and increase with research up to higher numbers. (If people really want to have a belt that always carries 2 iron, 2 copper, 1 steel and 1 plastic, they can achieve this by using several such inserters in combination. With a single synchronized stack filter inserter it is possible to create one lane with a configurable ratio of 2 resource types, which is already much better than one resource type.) I think such a new element in the game would make belts more attractive.
- Similar to the synchronized stack filter inserter, there could be an inserter with two input arms and one output arm, and each input arm has one filter and one number of items to collect before both arms give the held items to the output belt in a clearly defined order. This can be more intuitive than the synchronized stack filter inserter.
- Make a "lane joiner" that takes input from one belt (both lanes) and gives output to one lane in a way that it blocks input until two items are available on each lane and then both items are given in the same order to the output lane (left or right lane could be configurable). This is much less powerful than the synchronized stack filter inserter, and also easier to understand and use. It would enable designs where one belt contains four resource types in 1:1 (with complex combinations of lane joiners also other ratios) and if one resource is taken more fast from the lane than the other one, it would require to recover these resources in a kind of "overflow" lane that brings all kinds of resources back to the beginning of the factory where they are sorted with filter inserters into the right lanes.