The Edinburgh Gunners man has been one of the few highlights of the Scots' disappointing start to the RBS 6 Nations tournament.
But Saracens stand-off Castaignede insists Taylor - and Scotland captain Bryan Redpath - deserve credit for their performances in the 38-3 defeat by France on Sunday.
He said: "I have seen Simon play many times and played with him with the Barbarians.
"He will be a legend - he is just 23 and playing fantastically for Scotland.
"He was creating all the danger for Scotland - he put the team in the right areas.
"And Redpath looks like he has glue on his hands, the ball always sticks. These are two good players for Scotland.
"We won this game but we were not totally satisfied with the performance because Scotland caused us a lot of problems."