grub: monumental installation time waster

Anyone here know if there is any way to make GRUB_DISABLE_OS_PROBER="true" effective at the outset, before the installer does anything else? I tried adding it to /etc/default/grub before beginning installation, but it was quite obviously ignored until shortly before completion. The Mint 19.x installer spends more time on probing/Grub (including core-dumping python3.6), which is unwanted and unneeded in a something else/use existing partitions process, than the whole rest of the installation process. Grub.cfg grew to an absurd 167,696 bytes before /etc/default/grub's addition may have been taken into account. It's hard to be sure if this is the reason why, because the installer dropped freespace on / to 2% by the time it reported completion. /var/log/installer/partman is 4,876,050 bytes, 160,654 lines, of which 74,757 include parted_server, and 75,038 blank. Total uptime was 97 minutes, of which I'm guessing maybe 20 minutes was not devoted to Grub and partprobing. :(