Senior managers from Wales' biggest newspaper publisher have been defending their decision to cut 38 jobs before the assembly's culture committee.
The company produces a range of newspapers
Trinity Mirror executives also rejected the culture minister's accusation that their serious coverage was "a joke".
The Western Mail's editor Alan Edmunds said that was unfair and difficult to back up. He added they had to make changes in order to survive.
AMs rebuked managing director Keith Dye for heckling a union official.
Unions and politicians had already reacted angrily to the plans by Trinity Mirror, whose papers include the Western Mail, South Wales Echo and valleys-based Celtic group.
A report commissioned by the National Union of Journalists (NUJ), which was presented to the committee, claimed Trinity Mirror made profits of over £200m in 2004 and 2005, with the regional press "the most profitable, and this is specifically true in Wales".
Trinity Mirror chief executive Sly Bailey declined to address AMs
But speaking in the assembly's culture committee, the two managers said the position taken by the unions was based on conjecture and opinion, and littered with factual inaccuracies.
They insisted that despite historic levels of investment in Wales, and an increase in circulation, the decline in advertising revenues had forced a review.
Mr Edmunds denied there would be any impact on national and political coverage in the Western Mail.
He rebutted a claim by culture minister Alun Pugh that opinion formers in Wales regarded the Western Mail's "serious" coverage as "a bit of a joke".
Mr Edmunds said: "To say that opinion formers regard the serious coverage as a joke is an easy thing to say, but I speak to many opinion formers and they don't say that to me..I would suggest (it is) probably quite a difficult thing to back up.
"The serious coverage in the Western Mail is now more challenging...it's written in a less turgid manner, it has headlines that are more engaging. There's a lot more humour in the paper and there's a greater variety of stories."
Jeremy Dear, general secretary of the National Union of Journalists (NUJ) told AMs that given increases in circulation he was at a loss to understand why job cuts were necessary.
There was disagreement over the level of job cuts, with Mr Dye insisting the 38 posts reflected 5.5% of the Western Mail and Echo workforce.
But Andrea Jones from the Amicus union said later if job losses at the Western Mail and cuts at the printing press were considered together, then it was 10%.
As she spoke, was challenged over the figures by Mr Dye, who was in the public gallery.
At the end of Ms Jones' presentation, the committee's chair, Rosemary Butler, said she wanted no comments from the public gallery.
Rhondda AM Leighton Andrews said he had never known an outburst such as Mr Dye's at a committee meeting, and asked whether Mr Dye should be escorted from the room.
Mr Dye had represented the company at the committee hearing after Trinity Mirror's chief executive Sly Bailey declined an invitation to speak on the grounds she could not "add more to the committee's review".