Bit of an exaggeration on some of those.
Matthews is close to a top 5 C. It's not a reach. Top 10 if you prefer.
Tavares is easily a 1C.
Marner is close to a top 10 winger
(finished 5th in points among wingers last season and was on track to do the same this season before injury) but the contract is rubbish IMO. HF had a vote last season and put him at #11.
Forward depth was indeed excellent
(the team finished second in Goals For, 6th in PP%)
Leafs only have one top-pairing defenseman
(Rielly). Muzzin is a good #3. This is agreed upon among Leafs fans and is the number one priority heading into the off-season. That's why there's the hype behind Pietrangelo.
And no, Nylander is not a 1C or a top 30 forward. But he's a solid, young asset with a good contract.
You're right the team didn't do well in the playoffs
(technically didn't qualify for them ) but that has nothing to do with the quality of the listed players.