Caveat: I'm more playing devil's advocate here than actually advocating for the move. I'm on the fence about it because I think it may or may not work out depending on what additional moves are made but...
In a vacuum, I don't think 22 million per is an overpay for FVV's 18,7 and 4 if you believe he can maintain that production outside of the Raptors. He also addresses multiple needs. The Knicks need more playmaking and spacing; this guy is a career 39% three point shooter who took 7 attempts per game last year. He's also only 25 years old, so the Knicks would be bringing in a veteran with championship experience for his full prime if they got him. He's also one of those flexibility adds. He can be the lead or off guard (we know the lead guard thing from when Lowry got hurt last season). I prefer him as the secondary but his lead guard numbers speak for themselves.
This type of move also takes some pressure off of the front office to draft a PG. If BPA at 8 and 27 are different positions, the Knicks can make the BPA pick rather than forcing themselves to fill a need. Top that off with the fact that adding FVV to address the PG need doesn't cost the assets that a CP3 trade or any other trade would require and this could fill a need while keeping all of the picks in place to either use or try to flip in a separate deal (a CP3 + FVV scenario was tweeted out yesterday that technically works).
The downside though...the Boston series wasn't pretty, he may be a system guy and he's undersized although he doesn't really back down on defense. The Knicks need talent, but they run the risk of being stuck with another overpaid player that looked good in a proper situation and then flops with them.
That said, I'd assume the synergy between FO and Coach is partially why this rumor has such voracity. I've been half joking about bringing in Augustin because Thibs loves a short, quick, savvy PG running his show and has had success with that type (Augustin being the best example of overachieving). FVV is a better version of that imo, so I could see Thibs being the driving force because he's built offenses for this style of guard to run before. If we're looking at past examples, he'll want a high IQ big man that can do some handling and passing too. I think the Horford rumors fit that bill.