The problem is not the bute, its the person measuring the bute. If you can accurately measure out the correct dose it is just fine. Problem is how difficult it is to measure such a small quantity.
Banamine and bute are very different. They are both NSAIDs, but Banamine is targeted more towards soft tissue pain and bute is targeted more towards joint and feet pain. Giving banamine for hoof issues isn't useless, but it is not close to the efficiency of bute.
The dosage for bute is 1-2 grams 1-2 times a day for a 1000lb horse. No vet I've ever worked with has suggested I use such a high dose unless its a huge injury for a very short time. Two grams per day is the max I'd suggest. For a mini, that'd be .1 -.2 grams per 100lbs per day.
For Banamine the dosage depends on the form its in. Injectable is normally 1cc in the vein per 100lbs per day. Paste can vary, usually a tube is 3 full doses for a 1000lbs horse.
Next problem is estimating the weight of your pony. This can be just as hard as measuing bute! My very trim 38" stallion weighs in at 300lbs on a good day, measured by a livestock scale. A fat 38" pony could easily top 400lbs, and a trim 28" could easily be under 200lbs.