When Henry first arrived he took 6-7 games to adapt then there was no stopping him.
Walcott has had 5 years+
I saw Henry in the 98 World Cup and could see he was a terrific player then, he was also very good for Monaco.
Walcott just doesn't have the skills Henry has and never will have, like I said before his asset is pace, he's a little predictable but it's useful sometimes especially when teams become tired.