Two tiers are more than enough. If you own a quality target list (you can purchase a premium link list and sort it out yourself), you can use it with good content.
Nowadays, it's cheap to build a new site with AI and then use it as a buffer site, blasting GSA links to the buffer site. This works great with Reddit and Medium, but I'm considering creating AI sites and treating them as T1.
I do agree with Ranker X support. But I recently purchased Ranker X for testing, and it's quite a good tool. I am a heavy user of GSA SER and tried SERlib but never liked it. Therefore, I am now using Ranker X and GSA for T2, and sometimes I find high-quality links with high DA links, which I even use for Tier 1.
I wish Ranker X support was better and the price lower. I am going to use it for a month and keep continuing what I have been doing with GSA SER.
I'm looking for an automation tool to automate Blogspot and a few others since I found a nice way to dominate my niche.