Except you have to tank in the right year. The Edmonton Arizona Colorado Buffalo Columbus and almost all other basement dwellers for the last decade show that your magic bean theory doesn't equate to real life success unless you're lucky.
Toronto is not pushing the playoffs this year without Matthews. Mariner and Nylander are nice prospects, but getting the top pick and generational talent is the difference maker to building a team that way. Edmonton isn't where they are without McDavid.
Most top 5 picks are like Landescog, Nugent Hopkins, Reinhardt... Quality talent, but with the pressure to perform right away and without the right mix of coaching and veteran leadership, don't seem to be difference makers and live up to their potential.
To the point at hand, the Bruins have a bunch a forward prospects close to being ready or at least given a shot in the next two years, more than they have roster spots for with the veteran long term contracts in place. They will have to move some before they lose their potential playing in the A for too long.
Debrusk will get some looks next season, if Bjork signs he will start with the BB, Gabrielle and Senyshyn will be with PB, maybe even JFK. Cehlarik will need to get a long look next season, Heinen too. Time to move some is coming real soon. But I question whether adding a long term winger, even a quality one in Landescog, is the right move, without dumping Beleskey, Spooner, Hayes from the equation.