Of course they can.
I'm just saying with the following players who were in average form, suddenly being in this exceptional form in Europe, the quality of Top 14 and the premiership needs to be questions:
Julian Salvi, Leroy Houston, Mark Chisholm, Dean Mumm, Drew Mitchell, Matt Giteau and that's just off the top of my head before mentioning players that couldn't get a run here only to excel there like Brock James.
How often has a good player really struggled to make an impact? Rarely. It's pretty common for a player to be in even more amazing form than when they left Australia though. They must just have really good coaches I guess.