I have been on a long quest to upgrade my hardtail mountain bike. I have an upgraded Trek 4300 that I mainly use on unpaved gravel and dirt roads. I want to move onto a nicer frame and am very interested in nice steel frames, but am ok with aluminum as well.

What i am discovering is that as you move up the ladder on most manufacturer's product lines, you also generally move to more of a race geometry in their mountain bikes. Trouble is, I am more interested in having a relaxed geometry with a more plush ride. I am considering steel for the "plushness."

Am i correct in assuming that buying a "better" frame is going to get me a bike with more agressive geometry just about every time?

look at these bikes:

https://www.somafab.com/

Well, that depends on what you call "aggressive geometry". Your 4300 likely has 70.5/73.5 angles, which give it an easier-handling front end compared to a 71/73 bike, and will also push you slightly farther forward. If you're not looking at full suspension, most hardtails [steel or otherwise] will have 71/73 angles - companies have been using that geometry for 10+ years - it works. If the steering on the bike feels too darn twitchy for you, get a longer fork. Not 3" longer, but maybe go from a 85 to a 100mm fork. For the plushness, get bigger tires. You can be riding a frame made out of cement, and it will still feel plush on 2.5" tires at 30 psi. Honestly, I'm thinking of going from 2.1" tires to 2.3" as much for the feel as anything else. Other options for steel bikes include the Kona Explosif, Surly Karate Monkey, Rocky Mountain Blizzard and Hammer, etc. I think the Blizzard and the Hammer both have 70.5 head angles for a more relaxed ride.