A Q&A website has essentially two purposes: A) Help the OP, by answering the OP's question in a way that will be useful to the OP and B) Offer a service to the current and future community, by answering the question in a way that may be of value to the community in general.
Purpose B permits any level of mathematics while purpose A requires a level of mathematics that can be handled by the OP.
If purpose A is not satisfied, then the OP and its question is turned into just an excuse for posting Knowledge on the web, (and I don't believe that .SE communities view OPs in this way).
If purpose B is not satisfied, then the answer has not reached the "ideal".
From the above it seems clear that the answer should always include a part with a mathematics level that seems understandable by the OP (except of course for cases where it appears evident that the OP really knows nothing of the concepts included in the question, in which case the most helpful answer would perhaps be to point out the concepts that the OP should study first): Purpose A is satisfied.
If the same answer can be provided in a more general, elegant, insightful etc way using higher-level mathematics, then the answerer could/should also include this alternative answer, in order to also serve Purpose B above.
If the question posed cannot be answered at a mathematics level that suits the OP, then at least Purpose B should be serviced, and the answerer should go ahead with the only available alternative, i.e. an answer at a higher math level, so at least the community can benefit from it (Purpose B). But here, the situation should be explained to the OP , so that the OP understands that it is not out of a desire to show-off that the OP gets an answer that (s)he probably cannot use.