is it possible to write an iRule redirecting http requrest based on URI, but doesn't require http/fasthttp profile support?

Try throwing some logging in place:

 
 when CLIENT_ACCEPTED { 
   TCP::collect 
 } 
 when CLIENT_DATA { 
   set idx [string first " HTTP/1." [TCP::payload]] 
   if { $idx < 0 } { 
     if { [TCP::payload length] > 2048 } { 
        log local0. "ERROR! Could not find HTTP request in 2K! dropping..." 
        reject 
     } else { 
        Not enough data yet; collect more 
       TCP::collect 
     } 
     return 
   } 
   set request [string tolower [TCP::payload $idx]] 
   log local0. "Got request: $request" 
   if { $request contains " /XXXXX" } { 
     log local0. "Sending to Pool_XXXXX" 
     pool Pool_XXXXX 
   } else { 
     log local0. "Sending to Pool_WWWWW" 
     pool Pool_WWWWW 
   } 
 } 
 

This will log the each request right before checking it, so you can see if it you're getting what you expect.

One thing that I can think of that might be happening: the request is made all lowercase, so make sure your " /XXXXX" value in the if statement is also all lowercase.