The issue though is that right now, no single class/subclass mix really represents the concept well.
As for Witch, you have to deal with the stereotype that only females can be witches, so in the early days of D&D, when the vast majority of players were male, of course a Witch class failed.
One could.You could make the same argument about paladin, ranger, or druid, not to mention necromancer, assassin, or cavalier.
See, that sounds exactly like a warlock. I'd say that the focus on attack magic you mention later is more because they're built for PCs who are going adventuring, not PCs who are more stay-at-home, like your typical witch.So here are my brainstorm thoughts on this. They are a little raw...
Witches are spellcasters who learn their magic from some alternate way, and that alternate is a little... unsettling... to others. It could be magic from fiends, hags, deities, or the like, or some manner of folk "old" magic. Their magic is a little bit strange, even if the effects are like what a normal spellcaster produces.
As far as effects go, a witch's magic focuses on charms (robbing people of agency), curses (robbing them of ability) and polymorphs (robbing them of identity). There are secondary themes of nature (a witch is often rural and has some ability over the land), divination, and summoning (fey, fiends, shadows, the like). Tertiary, healing/herbalism and a touch of necromancy and general spellcasting (flight, etc.) round out the package. The thing I feel is that a witches magic is a little more subtle than traditional wizardly magic; some have said closer to a bard's list mixed with some of the spookier parts of the warlocks, but lacking the raw evocation damage that warlocks, wizards, and sorcerers are known for.
The Warlock trying to pass herself off as a "Sorcerer"? She can probably pull it off, as long as she sticks to the boonies and avoids people with a high enough Arcana to tell the difference.
At this point I feel I'm just repeating myself...Two points. First, what's "the concept"? As I tried to point out, there's a lot of flavors of "witch" possible and it's as hard to get people to agree on which should be the definitive one as it is to get then to agree on a definitive psionics model. Second, there's degrees of escalation and I feel you should start at the bottom and work your way up only as lesser steps fail. First would be using existing mechanics with a flavor reskin, then might be a new subclass for an existing class, and past that a new base class. The last of which, I'll remind you, needs to be able to support at least three or four subclasses to justify being an entirely new base class.
A subclass could focus on "circle" magic and rituals.