Confused with new Quota Tier's VertexAI / Gemini APIs and 429 vastly reported last 2 weeks

As recently noticed, even here on this Forum, 429 is back hunting us. So I started digging for info and I came up with a few questions since I am a bit confused: on my gcp account I have been using vertex ai. But I have been receiving a deprecation notice.

I started using Vertex AI because I have Startup Credits and, as far as I was informed about 1 yr ago, Gemini API is not covered by credits.

Then, this 429 thing again and the new Standard PayGo Tiers. I have gathered 2 pieces of info on this Forum: someone said Vertex AI is 2-4x slower… another fellow said he actively(?) migrated to Tier2 and still 429 (reportedly under limit usage. My GC’s Acc Executive have not been helpful for the last 6m. So i came up to this forum w/ this few questions:

1. Should I migrate to Gemini API since Vertex seems to be deprecated?

2. Will it be covered by credits?

3. Do I need to actually migrate tiers of GCP does that automatically?

4. Since there is this folk tell us even on higher tiers and even way below tier limits he is still getting 429… is it a temporary issue or there is more to be done?