The best way to find if your question is a duplicate is to use a filtered Google search. Put the key terms of your question into the search box, e.g. slowking
and flamethrower
in this case, and then add the filter site:pokemondb.net/pokebase
to make the results only include pages from PokeBase. Most of the time, this will bring up the question you've got if it exists already. It works for the question you asked.
Improving the related questions list is easier said than done -- there is an entire field of computer science dedicated to finding search results that are the most relevant to input queries. Naturally, Google has a better grip on that than an open-source project like Q2A, so if you really don't want to post duplicate questions, then checking a search engine is the best technique to use.
Though, as KyokaSuigetsu alludes, it shouldn't be too much of a worry if your post gets removed as a duplicate. It means the answer is already there for you on the site, which is only a good thing, right? I can understand it feels silly having your posts closed, but that happens all the time. Try not to stress too much about it.