وَلَا يَجُوزُ تَقْدِيمُهُ، أَيْ تَقْدِيمُ الْمَقْصُورِ عَلَيْهِ بِإِنَّمَا عَلَى غَيْرِهِ لِلِالْتِبَاسِ
In the described innamā construction, advancing the restricted-to constituent ahead of the others is ruled out because it creates ambiguity.
إِنَّمَا ضَرَبَ زَيْدٌ عَمْرًا
It was ʿAmr whom Zayd struck.
Moving ʿAmr immediately after innamā disrupts the clear association of the final element with the restriction and can obscure what exactly is being singled out.
This is an argument about the rhetorical interpretation of qasr, not a blanket denial of every syntactic fronting construction in Arabic.