Couple of thoughts...
You might have been over-optimized on that one keyword, which would make the jump up after removing seem right. Clean that up to focus on more synonymous terms, so you're not over-optimized on one keyword. That also might explain why the sites ranking ahead of you are doing well despite not having that specific term in the title tag/page copy. If you look at "Searches related to..." at the bottom of the search you'll see many of those keywords appearing in the sites ranking ahead of you. Google doesn't just focus on that one keyword, but also uses synonyms/related terms to help determine what the page is about. Using terms like "logo design software" or "logo design company" may also give users a better idea what the page is about, so they're more likely to click through to that page and trust they're going to get what they wanted. Look at the backlink profiles to see what their anchor text is like. That would also help you determine what kind of keywords other people are using to reference your competitors.
There's a ton of factors at play, but I think the main point is that you'll need to diversify the targets a little more moving forward.