Keep GodlessAstronomer's advice about the adjectives in mind as you're adding new text to this letter.
"advanced Excel skills" made me chuckle. I'm an engineer/researcher type, and maybe it's different for finance people. I do realize that Excel is more powerful than the world and 99% of the people who use it don't know 99% of what it can do (me included maybe). Even so, "advanced Excel skills" sounds a little pathetic. I'd go with something like, "at *Company 1*, I analyzed trends and anomalies in financial research from member firms," or, "I wrote code/software/macros/whatever to analyze..."
I don't know about that word "spearheaded"... it's got me thinking about mounting an attack through the desert or something. Tone it down. Maybe "oversaw," "supervised," "was responsible for," or "led a team" or something like that.
Nix the word "significantly" in that sentence. If you want to show them "significant," then tell them quantitatively how much you improved the process. 3%? 25%? 10,000%???!! If you can't quantify it, then just don't say "significantly".