That's the verdict of Paul Robinson who believes the Blues would have tried ‘very hard’ to keep the centre-back at Fratton Park.
Whatmough is supposedly poised to complete a switch to the DW Stadium on a free transfer despite being tabled fresh terms at Pompey.
The academy product, 24, was seen as Danny Cowley's priority when it came to the out-of-contract players, albeit he was offered a reduced wage along with Tom Naylor, Ben Close and Ryan Williams.
Whatmough was a key man as the Blues' play-off bid just fell short this season. After bouncing back from a third serious knee injury of his career, he made 37 appearances, scoring once.
Robinson, who played alongside Whatmough at PO4 along with coaching him when part of Kenny Jackett's backroom staff, reckons the package Wigan have offered might be better tailored to the Gosport lad's needs.
And it represents a big blow to Pompey.
Robinson told The News: ‘It would have been a tough decision for Jack, being a Gosport lad and being at the club since he was a youngster.
‘But maybe it might be good for him to get out of his comfort zone and his home city to develop as a footballer and as a person at Wigan.
‘It is tough times when you go through injuries. It's been tough for Jack when you go through one injury then get another.
‘What he has shown is what he has always shown on the pitch – that determination and hard work to get himself back fit and get back out there.
‘When he does that, he's a really good player and one Portsmouth will be gutted to lose.
‘I think he is an excellent League One defender. Perhaps the only reason he hasn't gone to a higher level already is because of his injuries.
‘There's no doubt in my mind he would be and you've seen how much Portsmouth have struggled when he hasn't played. When he wasn't available for some of those crucial games (due to suspension), you saw that and it's maybe why they ended up just missing out on the play-offs.
‘Like everything, there are different factors. It might do him good to test himself at a different club, that challenge of moving to a different part of the country and settling in.
‘People underestimate Wigan, they are a recent Premier League club. It might be seen as a League One to League One move but I'm Wigan have ambitions of getting back there soon.
‘It's such difficult times (because of Covid) and everyone has got to manage their situation accordingly. I'm sure they tried very hard to keep Jack because I know how well thought of he was there.
‘I'm guessing Wigan came along and then perhaps the whole package is better suited for him and his career moving forward.’
Whatmough's injury problems are well documented, having undergone three knee operations by the age of 23.
However, he made his most appearances of any campaign this term, proving anyone who doubted his fitness wrong.
Robinson had a serious knee setback himself during his playing days at Millwall, but still made more than 500 career appearances.
The 41-year-old feels Whatmough can continue without breaking down again.
Robinson added: ‘I think he can. What he'll have to do is put a lot of prehab in, taking rests when needed and keeping on top of the maintenance.
‘I know it's like carrying a bit of baggage but it becomes part of your everyday routine to strengthen the areas where needed to keep you on the pitch as much as possible.’