At this point it is, you are correct, but that will change when a few things happen.
#1--Kobe Julien coming back. Kobe is not as physical as Lewis or Brown, but can give you minutes that will spell one of them, specifically Lewis.
#2--Joe Charles and Isaiah Richards have to continue to improve and I think they will.
#3--We are playing allot of guys right now (10/11), that won't be the case when conference play rolls around, by that point your rotation will be 8. Here is what I see.
PG--Fulks
SG--Garnett
SF--Williams
PF--Lewis
C--Brown
Bench will consist of:
Julien if and when healthy
Charles
Thomas as you will need a backup PG but his minutes will be limited unless foul trouble
Dalcourt
You will see others play spot minutes, but the 9 listed above will gobble up the majority of the minutes. Thomas' minutes will not be as high as they are now and much of this will depend on the health of Kobe. If he is ready and 100% this team becomes much better.
Just my opinion.