FWIW, I’d rather not be tempted by making it too easy.
I’ve learned there’s often a reason for a particular English word to be the preferred answer for a meaning.
User synonyms are great for occasional use, and I’d hate it if the feature were removed, but I do feel it’s awfully easy to abuse (I know people have used it to add the transitive/intransitive pair for every verb, for example).
Today I answered “analyze” for 析 (analysis), for example. I actually created a user synonym but then later thought better of it and deleted it. I’m familiar with both of the vocabulary examples (分析 and 解析. Alone, they both mean “analysis” and while, for example, 分析する means “to analyze” I think it’s beneficial to memorize the bare-word 析 character as a noun rather than a verb.
Maybe not the best example, but there have been numerous occasions where not adding a synonym aided my learning.
I know WK is specifically focused on simply “teaching to read kanji,” but I also value several incidental benefits toward my goal of better speaking, reading, and understanding Japanese:
The size of my vocabulary has increased.
I’m better able to understand the nuanced meaning behind words I thought I already “knew”.
I’m often able to read, hear, and understand even 熟語 that isn’t taught here.
In addition to recognition, I’m also able to produce Japanese words better. In other words, both my Japanese comprehension and my spoken Japanese have improved.
I doubt everyone will agree, but I believe forcing yourself to memorize the specific English meanings WK provides is beneficial (as long as you actually understand which specific meaning of the English word is intended — not always easy!). Memorizing those specific words will never be wrong.
I try (but often fail) to fight my urge to create a synonym unless I’m absolutely certain it makes sense. I’ve occasionally discovered I misunderstood the meaning that was intended, and adding a synonym might have made it even more confusing.
To me, mentally filing a Japanese character or vocabulary item under a subtly wrong “synonym” would detract from most if not all of these side benefits.