I appreciate the way you have handled this discussion. There is actually a better stat than assists that can indicate value to your teammates: +/- . That stat has limited application. It's meaningless to compare players between teams, or even players on the same team if there are few games, but it is meaningful to compare players on the same team with a large number of games.
Assists is problematic for the very reason I already stated: context matters. We all know Taurasi can score, she proved that in the WNBA, yet her pride and joy were assists and she was the record holder up until recently. Her assists do not match Ionescu's for three reasons. 1. In Taurasi's era the UConn offense was more post oriented. In fact, in the 2002 championship game we went 0-9 from three. It's a helluva lot easier to rack up assists if you can feed the perimeter at least as much as the post. 2. UConn's offense is built on versatile players reading and reacting, that is going to spread any statistic around, the previous point I was making. 3. Despite this versatility, for two years Taurasi's backcourt mate was Sue Bird, who went on to become the WNBA assist leader. Indeed, if Bird had not just played 8 games her freshman year she probably would still be UConn's assist leader.
In lieu of assists or a +/- for comparison I offer you one final anecdote to provide clarity for what you seem puzzled about. In Taurasi's junior year she was the only returning starter. Two starters had seen limited action their first two years while the other two were freshman. They only lost one game and won the championship despite that handicap, but it's what happened in one particular game that proves Taurasi's worth. We were down to Tennessee late in the game, I believe by 6 points. As Auriemma tells it he was prepared to now consider the game a learning experience for his young, inexperienced squad. When he started to convey this sentiment during a timeout Taurasi looked at him like he had two heads and huddled up her teammates without him, rallying and convincing them they were going to win the game. She then proceeded to make a three from about 30 feet, along with some other heroics, and UConn won the game.
The past three semifinals were close ones, two lost in the final seconds. You will not find a single UConn fan that thinks we still lose those games if Taurasi was one of the five playing at the end, no matter who you subbed her for, Collier, Samuelson, whomever. More important, there is not a single teammate of Taurasi's through her college and pro career who would doubt her ability to win a game at the end. That is the basis for Taurasi's support.
For the record I think there are too many variables. I think a good argument could be made for Stewart as well as Taurasi, plus I am in no position to compare to someone like Miller from an earlier era.