This hits the nail right on the head, plus a "scale" plane like this performing an axial roll just looks wrong. A well performed barrel roll will present much better in the air.

A large contributer of making scale planes look good in the air is finding out what they do well, and practicing that. From my perspective there's nothing uglier than a scale plane being forced to do something it doesn't want to do and a T-28 doing an axial roll is one of them.

However if you absolutely must practice axial rolls with it, then the correct technique has been outlined in previous posts, where you need to co-ordinate the rudder and elevator to keep the flightpath straight. I'm a pattern flier who strives for geometric perfection and that constant speed look, but who also appreciates the beauty of a scale plane being flown true to scale which itself is no easy feat.

Good luck with the practice.