Rhinos finished ninth in Super League last year and had to battle for their top-flight future in the middle-eights Qualifiers.
Thirteen months after the end of one of the most traumatic seasons in the club’s history they beat league leaders Castleford Tigers 24-6 to win an eighth Super League title.
They exceeded expectations by finishing second on the table and reaching the final and were too good for Tigers - who finished 10 points ahead of them - on the night at Old Trafford.
McDermott insisted all along - even after a 66-10 defeat at Castleford in March - Rhinos could win the championship.
“To finish second I think was a huge achievement and to make the Grand Final in the fashion we did,” he said.
“I think the group, led by Magsy [captain Danny McGuire] has been great and to win the Grand Final, I am lost for words.
“It is crazy - and not just win it by a thin margin, we were pretty dominant. When a group of people go through so many emotions together like we have over the last 18 months, you become a strong group.
“Castleford have been more skilful than us this year and have put on better shows this year, but I would question anybody who says they’ve had more commitment than us this year, certainly towards the back end.”
McGuire was a unanimous winner of the Harry Sunderland Trophy as man of the match, in his final game for Leeds before joining Hull KR next year.
He has played in all Leeds’ eight Grand Final wins and was also man of the match against Wigan Warriors two years ago.
He said: “It’s a fairytale. You want the fairytale ending, you want to win and play well, but you realise there’s a lot of hard work to do before that.
“I thought the boys were unbelievable, from one to 17. We spoke all week about not leaving anything out there and the commitment and work ethic was unbelievable.
“Obviously I am really pleased with the win and I am going to enjoy the next few days, definitely.
“I was really determined to make sure my Leeds career finished on a really positive note and winning a Grand Final, it doesn’t get any better.”