Rangers would trade him to get more

If 1 year of Freddie Andersen gets 15th overall, Rangers match

Good luck getting a 2nd for a 28 point player who isn't that young. Florida declines.

A goalie who will be 32 when the season starts, being traded by a team who's fanbase is seemingly demonising him does not fetch 15th overall.
He didn't fetch that when he was 5 years younger when the leafs traded for him. That year there wasnt a flood of goalies on the market and a cap crunch.

I kinda think so, but don't the rangers have a lot of other guy to sign? so just seemed easier to offer sheet.

Freddie's become a proven number 1 in his time with the Leafs, he wasn't with the Ducks

Bingo. They love to dump on/blame it on Freddie until it's time to trade him, then he's worth 100x more since he wore that Leaf...

So, there isn't much of a precedent for a proven starter who has fallen out of favour with the fanbase and is on the wrong side of 30 being traded,
Best example I can find is the Luongo deal back in 2014, he fetched Shawn Matthias and Jacob Markstrom (who at that point had looked like a career backup.)
The problem with this comparable is the contract. Luongo was acquired at $4.5 million per year with 7 years left to pay (though it was a front loaded deal, so he had been paid more than half of his money.
It was cost controlled, and he did have 4 seasons in Florida where he was reasonably worth the money.
Cap wise this is obviously a poor comparison for Freddy, who is at $5mil, so proportionally less of the cap than Luongo, but in need of a raise next summer during an offseason where the cap will stay flat.

I am by no means suggesting Freddy will return Matthias and a backup, but there is no precident at all for freddy having this much value.
Curiously, the last case of a goalie returning a 1st round pick straight up was the original Freddie trade.

Excluding the lopsided trades, the only way leafs could actually make Petro work is if they move nylander or Marner

There is no reasonable way the Leafs can sign Petro and keep that top 6 and the 2 goalies you have listed. Those 8 players account for over $50 Million of the salary cap. That would strip the team of any depth they have and they still are at the cap. That's not feasible to win a Stanley Cup that way. I think the only way they sign Petro is if they make a trade or two from their core.