You answered your own question right before this: Florida has only had one playoff appearance and it was against a juggernaut. The Leafs have 5 straight appearances, the last two as favorites and lost both. Against Columbus in 4 of the 5 games they failed to score an even-strength goal. Against a big underdog the Habs they blew a 3-1 series lead. I'd say the pattern is pretty clear.
While I agree they have a strong core and should be contending, it's clear there are too many holes in this year's lineup to fix without severely hurting their chances down the road. I also don't buy that there is a small window for them to win, but by trading more futures Dubas is narrowing that window. Reilly signed an extension, they've got 2 young d-men improving, I believe Matthews will do as most elite players and re-sign with the team that drafted him. Marner likely will too.
I only suggest that given the current state of this team and how incredibly difficult the path will be, it's not the year to sell off more of the future and box themselves into a narrow window to win it all. I'd like to see if Dubas can get another veteran defenceman, but not at the price of a first/top prospect. When summer comes maybe take a shot at someone like Lindholm if Kyle can clear some cap space.
That we can agree on, not at the price of a 1st/top prospect, it's believed he is refusing to trade the 1st rounder for a pure rental like Giordano. But he should be looking to upgrade the roster, this team is very capable of beating Florida/Tampa. Even assume it was a 1-8 seeding, by the ECF you would have to go through one of the top teams, CAR/FLA/TB, we just so happen to have to go through one in the 1st round.
I strongly disagree with your idea that there are too many holes. There is only 1 glaring hole which is goaltending, but top 4D and top 6 LW COULD (not necessary) but COULD be upgraded.
Leafs are the 3rd highest scoring team, FLA is 1st
#1PP, #5PK, #5 overall in points, #5 overall in PTS percentage
The weakness has been goaltending and lack of PP opportunities. They have the 4th fewest PP opportunities in the league despite being the 4th best possession team. There is only 1 month this year (November) where we had .900+ svp from our goaltenders, every other month has been well below that.
Also if we learned anything from last years playoffs, anything can happen especially with freak injuries (Tavares) I'm not wishing injuries to anyone but say somehow there's a freak accident and Barkov goes down, the Leafs will now have a significant advantage in that series.
As a top 5 team, you absolutely have to take a shot to win. Not trying would just be pathetic "pack your bags boys we got FLA/TB we'll try again next year with an easier opponent, we're not good enough to compete with them" is essentially what you're suggesting and it's pretty ridiculous and offensive. Just a polite way of saying you stand no chance try again later, and I'm not having that.