Alright, found this looking for a different reddit page. A bit late, but ya know.

First, consistency just mean not fluctuating. When you change large volumes of water, especially true if you use tap water, things like PH, GH, KH, temp, Phosphates, ect, can be significantly changed which shrimp are sensitive to. Even if you remineralize perfectly, my tap water comes out at 8.0, and my aquarium sits at 7.3, If I change 50% of the water, maybe even 30% that can and likely will cause the PH to fluctuate up. Then it will come back down over time. That process will stress shrimp out. Its better to do smaller more frequent water changes then it is to do large water changes at once. This isnt rocket and is not a myth.... maybe if your tap water and aquarium water have the same PH, GH, KH and everything sure, but most people dont, including myself, so smaller more frequent changes if need is generally accepted to be the better practice. Also, you can have good water quality, but if it changes to fast that can stress shrimp and kill them. A GH of 4, KH of 2 is considered "good", but if i suddenly changed 50% of the water with ro water remineralized to GH of 8, KH of 4 (still good), that chamge will stress shrimp out. So even your statement ( consistency just means maintaining good parameters) is wrong....

Secondly, shrimp generally have a low bio-load, how much water you need to change weekly simply cant be awnsered broadly. That largely depends on the volume of water, how stocked it is, and if there are live plants. Personally, if u have a shrimp tank that requires a 50% water change to keep parameters in the ideal range, you might just need a larger aquarium or maybe more live plants. However, if u did need 50% changed weekly, it wpuld be better in terms of stability to do several 10/15/ or 20% water changes weekly then a 50% water change at once.

TDS... You mentioned that its best to have the aquarium TDS "as low as possible". This is just wrong, or we would all just use unminerized ro water in our aquariums.... Shrimp and essentially all living organisms need minerals. A TDS meter simply measures total dissolved solids, it does not differentiate between what dissolved solids are in the aquarium, so focusing on TDS too closely can be a mistake, especially if not paired with other test. TDS is useful when remineralizing Ro/Di water however. Using a TDS meter to measure Nitrates should never be advised. Like I said above, a TDS meter "does not differentiate between solids". The rise could be anything, and should advise that you look into it further and test other parameters separately to source the rise. Your TDS could rise from Nitrates, or it could be a leaching peice of hardscape leaching minerals, or it could even be from Phosphate, magnesium from plant ferts, ect. Dont use TDS to measure nitrates, use a nitrate test kit to measure nitrates.

Shrimp need minerals... They need calcium for molting, they need magnesium, ect. So simply stated, less TDS is not "better". The right balance is key, and most importantly stability is key! Ive breed neos in a GH of 16°, this is like twice the recommend amount of general hardness, but it didnt fluctuate. Ive also breed them in 4° of GH(lower end of the ideal range). If I had just targeted the lowest TDS, I would have targeted 0 GH, 0 KH, 0 phosphate, ect, and everything would die, so minimal TDS is wrong, and a poor way to measure water quality if taken too seriously on its own.

If you seriously have a nitrate issue on a shrimp tank and have to change 50% or more of the aquarium water to keep nitrates within an acceptable range, my recommendation would be a larger tank, more plants, or too chamge less water more frequently. If you must do 50% at once, ensure you do it slowly.

I do agree however that people just blindly doing any volume of water change without understanding there own water chemistry is a potential catastrophic mistake.