Nope, SQM and packet steering are entirely separate.
There is now an option in LUCI master with commit to enable or disable packet steering under Network - Interfaces - Global Network Options. Text indicates that packet steering "May help or hinder network speed" as not one size fits all.
@bill888 Have you setup proper interrupt balancing? You need the patches from topic Xrx200 IRQ balancing between VPEs, two for kernel 4.19 or one for kernel 5.4 experimental.
EDIT: Oops misread the update that your testing returned to 130 Mbps.