But bullish Scotland coach Hadden insists his men are on course to shock the defending champions at Murrayfield.
Hadden said: "Wales are the Grand Slam champions and rightly favourites for the championship this year. They have a star-studded line-up in both the forwards and backs but crucially, they have hardly had any injuries.
"They have had a settled side for the last couple of years and if we'd been like Wales, we would have made faster progress.
"We had a massive number of injuries in the last two Six Nations campaign and the injury list is mounting again.
"But we believe we've got the strength in depth which makes us competitive."
Wales have been installed as firm favourites for to reclaim their crown following last season's Grand Slam triumph.
Warren Gatland's men were handed a further boost when the Welsh regions agreed the Kiwi would receive 13 days preparation time with his stars for the daunting trip north of the border.
But the IRB eight-day rule applied for Scotland, just months after the Scottish Rugby Union had a stand-off with Premier Rugby over access to their English-based players prior to the autumn Tests.
Hadden said: "We would have loved to have had the amount and quality of preparation time that the Welsh have had. Regulation nine has not been kind to us in that respect.
"We feel we've learnt how to maximise the small window of opportunity we have available to us and I'm really happy with the way preparations have gone. We're ready for Sunday."
More than 1,000 tickets are still available for the clash in Edinburgh - and Hadden knows his team must prove a box office attraction to the fans.
Hadden said: "There's no doubt we've made huge progress over the last few months but that's not what the punters want to see.
"They want to see the scoreboard moving in our direction more often than we've been doing. We're fully aware that we need to deliver more wins.
"It will be an extremely tough challenge for us but we believe we're more than capable of being really competitive against them - and beating them."
Scotland team v Wales: Hugo Southwell (Edinburgh); Simon Webster (Edinburgh), Ben Cairns (Edinburgh), Graeme Morrison (Glasgow), Sean Lamont (Northampton); Phil Godman (Edinburgh), Mike Blair (Edinburgh); Allan Jacobsen (Edinburgh), Ross Ford (Edinburgh), Geoff Cross (Edinburgh), Jason White (Sale), Jim Hamilton (Edinburgh), Ally Hogg (Edinburgh), Simon Taylor (Stade Francais), John Barclay (Glasgow).
Replacements: Dougie Hall (Glasgow Warriors), Alasdair Dickinson (Gloucester), Kelly Brown (Glasgow Warriors), Scott Gray (Northampton Saints), Chris Cusiter (Perpignan), Chris Paterson (Edinburgh), Max Evans (Glasgow Warriors).