I think I understand what you mean, and I talk about this under the pictures where I reference other ways that rely on more occasional tweaking instead of pump power.
The reason I prefer this to a valve limiter, is because it works no matter what the flows are. You also may not need this if your input arrives with very little head to begin with (as in your case with lower elevation sulfuric acid source). However, if both are near the same level and especially if the source is at high elevation, the extra power from the excess ensures it is always used first, with no future tweaking needed from a valve if inputs/outputs need to change.
It will most likely work your way as well as if you don't mind tending the valves, I just like to setup robust systems that have a lot of built in toughness/redundancy/flexibility/etc., even if it needs a little pump (costs power to further automate the system).
I love that this game encourages so many cool solutions and they can all work!

I have waste sulfuric acid feeding back to the mainline from below and it doesn't back flow, pumps act like a valve while giving you head lift, then just put a valve on the mainline before it merges and restrict it for the amount that is coming back

Ah, right on, hopefully it works for it!

I tend to build on raised platforms, and this can work without the extra raised structure, provided the output pump is higher than the "final" input pump, (might need to be tuned for height) and there are no other supply failures in the first stage production. I usually add a buffer tank so it doesn't just stop if there's an overflow, but if the I/O math is good, shouldn't be a problem. Nice work around for "flat" designs though, I'll keep it in mind. I have one setup that is output lopsided, I'll have to test if this works for correcting overages, that would be super cool.

P.S. I missed your caveat at the end, so apologies for calling it over-engineering! Most definitely one of the most unique solutions to an issue I've seen. Kudos :)

I think this might be a case of over-engineering? The idea is great, but I think you can accomplish the same result by restricting the flow of your main source using valves so that the excess can fill in the rest. EX: Recipe requires 105 water. Recipe produces 30 excess water. 105-30=75. Configure valve to max out at 75 and then tie the excess to a point on the pipe after the valve. I feel like I might be missing something so feel free to point it out!

Very welcome! Oh wow, that manual is quite thorough indeed. This game is so wild. I was surprised how much of my background knowledge helped and I see they did a pretty good job modeling it.

Thank you for the tip!
I also recommend: Plumbing Manual: Overview
Made by: @McGalleon#8273 (Discord) u/MkGalleon (Reddit)

https://drive.google.com/file/d/1MdZ8Xr8P_SF_FL7B6WDjCZGS-x9Cwt-x/view

Very welcome, hopefully it comes in handy!

I will try to use this in my next play-though, thank you for sharing kind gentleman!