I am still getting rate limit errors even with the throttling of the Q&ER extension. In the AV community discussions I saw the following which implies that you need to do about 10 calls and then wait 10 seconds. The 10 calls can be quick, but then need to wait??
https://www.alpha-vantage.community/post/rate-limit-question-9682398

It depends on timing between calls, or rate of number of calls per seconds. When you start, 1st call is considered as one call yet. After you placed about 10 requests, consequent or parallel, the rate of the call frequency kicks in and you get either 503 response (server error) or short 200 response with the warning that you place too frequent requests. Recently it is about 10 seconds between requests (or 0.1 requests per second rate) that you have to maintain in order to avoid those errors.

I believe the reasons for degradation are that service became more popular, though hardware and network resources available to process the requests are not upgraded. I would be happy to mistaken.

spassiba