That's not true. No shell is involved in the second snippet. (Check the ppid of ps.)

$ perl -e'system "ps -opid,ppid,cmd 2>/dev/null"'
  PID  PPID CMD
11096  7077 -bash
 5166 11096 perl -esystem "ps -opid,ppid,cmd 2>/dev/null"
13220  5166 sh -c ps -opid,ppid,cmd 2>/dev/null
19387 13220 ps -opid,ppid,cmd

$ perl -e'system "ps -opid,ppid,cmd"'
  PID  PPID CMD
11096  7077 -bash
13513 11096 perl -esystem "ps -opid,ppid,cmd"
26826 13513 ps -opid,ppid,cmd
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