Exactly, you got the point! The translation was definitely not straightforward, yes I extended SymbolicUtils pattern matching this summer, creating the “defslots” that allow to match a pattern with some default values, and improving the handling of commutative pattern matching. Also I improved pattern matching of powers with negative exponents, that was quite difficult and still not completely solved. Here you can read in more detail.
On top of that the old SymbolicUtils pattern matching was too slow to handle the thousands of rules I needed, so in the last weeks I rebuilt it from scratch improving ttfx from 14 min to 12 sec! I am so happy about it, on my blog post you can read in more detail