This is actually only a restriction imposed by whomever created the Hubspot app on Zapier.
Zapier may be the ones to own/maintain the App, or it’s Hubspot (new Apps are almost guaranteed to be the App owners themselves, whereas Zapier had created the first 150+ or so, and Hubspot is an old App).
Odd that their support didn’t recommend putting in a request for the feature (Instant Trigger for New Deal), since the Hubspot API and infrastructure supports it via their programmatic Webhooks. Not only that, but the Zapier Hubspot App clearly already leverages the Webhooks. It would be a few hours of a dev’s time to enable “New Deals (Instant)” for you if they know what they’re doing and they’re just adding to the existing App.
I’d recommend reaching out to Hubspot support directly and asking them about it. Feel free to point them to my response here.
If you don’t get any help and time is of the essence, my company (Left Hook Digital- lefthookdigital.com) could help you out. It’s more cost effective and better for everyone if the App owners make the improvement, however… so while we’d like the business I’m hopeful that you’ll get help! Or if they can’t get to it right away due to product roadmap etc., we (Left Hook) could jump in and help; I’d just need to talk to the team.
Okay and one last thing; you can set Webhooks in the Hubspot Developer UI (see documentation here) and use Webhooks by Zapier if you’re trying to put in place a one-off Zap. Hopefully there is enough documentation around to help you out with that but if not feel free to reach back out here or via email/our website.