At 5 or 6 tailoring I still occassionally failed to reinforce items, and more rarely damage more complex items.
But I did succeed in repairing my clothing well before then. Sewing is highly dependent upon dex. As an alcoholic I have to stop and drink fairly regularly, and I have to watch what drink, because anything too hard (like moonshine) will dehydrate me and destroy my dex as much as any shake syndrome if I drink it enough to stay drunk.
Dex is typically my weakest attribuite to begin with too. Buff your dex, keep in mind the RNG is stll the RNG, and dont push waht you cant lose.
Im a little surprised that its not even harder. If 2-3 is considered competent by the game (it is, according to the factions menu and evidenced by professions in character gen) than 4-5 is proficient and 6 professional. iirc, thats what DF named its skill levels ;). this more or less falls in. Much better than before where it was possible to literally achieve a fully fortifed set of clothing (except for things like rucksacks which are thick, hard material and designed to actually varied carry heavy loads) on day 1, in about 12 hours. Im much happier with the effects of repairing things like steel spears too. I spent half a day with level 4 mechanics struggling with a spear to get it fortifed, but the crude makeshift crowbar was done in ten minutes.
Charge useage is more in line with ‘in between welders and before’. Fun fact, welders would use 50 charge per attempt to repair metal items.