Mate here are his stats as both a centre from rd 13 in 2014 when he was switched there and as a fullback for the full 2015 season.
2014 from rd 13 as a centre
Played 11
Try Assists 2 or .18 per game
Line breaks 9 or .81 per game
Tries 9 or .81 per game
Hit ups 142 or 12.9 per game
Tackles 194 or 17.6 per game
Run meters 1263 or 114.8 per game
Avg per hit up - 8.89m
2015 As FB
Played 21
TAs 2 or .09 per game
LBs 12 or .57
T 7 or .33
HU 377 or 17.95
Tackles 157 or 7.48
RM 3629 or 172.8
Avg per hit up - 9.62m
So going purely off stats and not what he does behind the defensive line, he gains 58 extra metres a game and has 5 extra hit ups to get those metres at an average 9.62m per hit up as a fullback.
As a centre in 2014, he made 73cm less per carry, had 5 less hit ups per game and averaged 58m less per game. He did however, with Beale and Quinlan at the back, averaged double his try assist rate, average .24 extra line breaks a game and nearly tripled his try scoring rate! To me this suggests he would be more dangerous playing centre but everyone is entitled to their own opinion and I feel we would be more dangerous with a ball playing FB and with the Dugan playing as a strike centre.
http://www.totalfootystats.com.au/nrl-player-stats/st-george-illawarra-dragons/josh-dugan#.Vk11Hv4gkis