The forbidding of JW sisters from wearing pants really has nothing to do with decency or modesty. The real reason is their antiquated male chauvinist view that pants is a man's clothing and women should therefore not be wearing them.
In Watchtower's twisted antiquated mindset, pants symbolize masculine authority so any woman who wears pants is encroaching, somewhat, on the male headship arrangement. She is either a domineering woman or she's a lesbian or at the very least, they would claim that that's the impression she might be unwittingly giving to others.
You mentioned that wearing business suits makes a woman look authoritative and well educated. Watchtower doesn't want JW women to look authoritative. Watchtower wants them to look submissive. Watchtower also does not want JW women to look well educated. Watchtower often associates being well educated, (secularly) with being opinionated and Watchtower doesn't want opinionated JWs and especially not opinionated JW sisters. Watchtower wants JW women to look like they should be - servile, naive and minimally educated. Anything more and the woman is overstepping the bounds of her God-ordained role of subjective servitude.