Kerfoot was exposed to Seattle while the 3 pieces going to Toronto in your post were not.
There's a slim chance the two picks might get you Nick Paul if he won't re-sign in Ottawa and no other team is interested in him before the trade deadline.
In that event, that leaves us with Logan Brown and Austin Watson for Alex Kerfoot.
Logan Brown can be had for a late 2nd/early 3rd while Austin Watson can be had for a 4th in 2022, considering we paid a 4th to get Watson in the first place.
Before the expansion draft, teams like the Vancouver Canucks were willing to pay only a 3rd round pick for Kerfoot.
That was until the Leafs acquired Jared McCann as a means of forcing Seattle to choose between him and Kerfoot.
That is only a brief explanation as to how there is way more value in this trade for the Leafs than for the Sens.