Yep, that would sure solve a lot of problems for the Canucks. Getting rid of the inferior Myers (compared to Holl). Getting rid of non value Boesner even at 5m
So in effect the Leafs give up three firsts and second for a rental Horvat.

Zero chance the leafs would do this. They lose all their D depth and get worse, and more expensive while doing it. Sure, the fwd lines look great, but 3 firsts is a hefty price to take on three underperforming players on high salaries

One trade... Meanwhile there are like 10 pieces involved

How are Horvat and Boeser under performing at over 1.0 and at .80 PPG respectively? And Myers does not have to do ANYTHING offensive - just hang back and play D to cover for Rielly

Underperforming to their contracts, if they're doing so well, why does everyone in Van want them out? And your description of what would be required of Myers is accurate, however, he isn't capable of playing defence. The Leafs are better off with Holl (at 1M less even with the retention) and Timmins as depth, especially with how well Holl has been playing with everyone out.

So on October 1, Toronto might have only Brock Boeser to show for this trade, having meanwhile given up three first-round picks, a second-round pick, a developing defense prospect, and three players that have SOME trade value.

Even if they win the Stanley Cup, that STILL seems like awful asset management to me, because they're unlikely to get there again for several years after losing all of those futures.