Bumping up the number of concurrent threads is an easy and effective way to reduce the timeouts you’re seeing, but responding more quickly will also help mitigate the issue. If your server can handle more concurrent requests, I would recommend increasing the number of concurrent threads. Additionally, you should try to optimize for the quickest possible response to HubSpot.
Regarding the batching of notifications: HubSpot only begins batching web hook notifications once they reach a certain number per second. Until that point, the notifications are sent as quickly as possible. e.g. if there are 3 requests in 10 seconds, we do not wait a full 10 seconds to send all 3. We just send each individually as soon as we process it.