It would be, but it sounds a bit unbelievable, unless Toronto are paying an insane amount for MLS, which would be kinda destabilizing. It would be a mega readjustment for the league, and all the big spenders would have to either play up to keep up with TOR or complain to Garber. It would be even worst for the teams like COL, Nashville, etc that have managed to stay relevant on a budget. It sounds a bit crazy, without knowing the terms of the next broadcast deal.
For comparison's sake TOR already have the most expensive player in the league in Pozuelo, who earns 4.6 M and cost apparently 11M in transfer fees.
Insigne is in a completely different league. He is the best player in one of the strongest teams in Serie A. There are many numbers flying around on the www, but it looks like his current annual salary is 9.6 million (Google and other sources say 5 M, but that sounds very low). Maybe at 30 he is looking for a last fat paycheck and only a less prestigious league like MLS is willing to offer a guaranteed 5 years at 12 million per year, which is the rumor regarding TOR. Obviously, more competitive leagues wouldn't take such a risk for a 30 year old. OTOH, Insigne is finally blooming at 30, arguably playing the best soccer of his life, a starter in the Italian national team, a star in the last Euro, etc. His valuation is around 50M (maybe a bit less because of age). He is literally twice as big in terms of current value as any previous DP.
I personally think Giovinco has been by far the best DP in MLS, and his profile was waaay lower than this. It is almost like Dybala deciding to come to MLS, except for the age.
