That's not taking a step backwards for one season. That's taking a significant step backwards for the foreseeable future, and potentially until another full-on rebuild unless Byfield/Clarke/unspecified prospect turns into things that none of them have shown to be.
That's very, very different from what Florida did. Florida exchanged a very flawed player entering his post-prime for another top-tier NHLer in his prime. They did not trade the reigning MVP in his prime for prospects and young players that are struggling to establish themselves in the NHL. Florida's not exactly excelling after that trade anyway, so weird thing to point to.
At the end of the day, if the Leafs sign all of Matthews/Marner/Nylander to reasonable contracts that you'll incorrectly call bloated, they'll continue to be contenders for the foreseeable future instead of destroying their team for no reason. None of them are starting any kind of serious decline soon, and this formula has shown to work to produce top-tier teams. You don't abandon it when you're finally going to get a rising cap and internal depth coming through.
Byfield is a 3rd liner playing at a 6 goal, 40-point pace, at an age when Matthews was already a superstar. You don't trade the reigning MVP for somebody with an alright 10 game stretch.
Clarke is having a good short season in the OHL as a 20 year old, but that's the OHL, not the NHL, where again, Matthews was a superstar at that age.
They are good prospects, but they are likely not going to become anything remotely close to Matthews, even if they become NHLers.
And they don't really fit the timeline you're creating around Tavares and O'Rielly.