Okay, story time again.
It is really not that hard, depending on what you want in terms of mods, of course. Some engineers are more annoying to unlock, but I found the process rather easy, to behonest.
My on-foot engineering journey went as follows: During 2022 I now and then took a dip into on-foot settlement gameplay to see if it was finally playable for me (it wasn't). During that phase I looted a handful of settlements that were easy to raid (the Arai's Mine layout) and built a kind of base stock of materials. I did that with store bought gear - a G3 Maverick, a G3 shotgun and a G2 tormentor. I then decided that it just wasn't there for me yet and put it on the shelf.
In early January this year (could have been as early as around Christmas, my memory is foggy there), after U14, I decided to revisit settlement gameplay and was pleased that finally I could approach a settlement in VR without instant headaches. So I made a list what I wanted. I used the brilliant Odyssey Materials Helper to make a wishlist of what I needed. I also had already made a "loot list" that told me what to pick up and what to leave behind, and I had found a Maverick with backpack capacity in the meantime, so that helped, but basically I set out to G5 and mod the Mav, the shotgun and the pistol.
I picked out a system I wanted to "work" in and just did missions for material rewards. Alot of delivery and salvage stuff at first, and a few powerup missions. Seeing that I was pretty able to deal with the scavs on the powerup missions I then went to combat missions and started doing raids and exterminations. I chose only missions that rewarded me what I needed. It was a slowish process, but not as slow as some tell their experience was - I did a few missions every night or so, and was slowly building my stock of materials.
Also, and that might be important, I learned what assets are a good pickup to trade and which ones are just a waste of space. Luckily, there is a certain overlap, some assets that trade well also dropped in spades in the settlements I was playing in.
The engineer unlocks were practically a by-product of my gameplay. It was a bonus that I could cheese a few with the help of my own bartender, but hey. I pay a lot of credits for that stuff, might as well get something out of it.
I did this for about three weeks, half a dozen or so missions on every play session. The important thing: I never did "grind". I just played, and I had fun. While I was collecting materials I also learned about NPC behavior, settlement layouts and strategies how to tackle which kind of mission - sneak in or go loud, where to go first, that kind of stuff. I played the game, and I had fun. I did cheese a bit and got about a dozen MI from thirty minutes of relogging on a satellite and about 60 weapon schematics from doing the same on a three-container site, but that's it in terms of cheesing it. At some point, it felt like the mats I needed were just rolling in.
Starting with G3 gear is definitely a must, but it is not so hard to find at least non-modded stuff. Apart from that, I think it is, again, a question of mindset. If you go by "in need to grind all my G5 stuffs as fast as possible", it sucks. If you just relax, collect and trade what you find in a smart way, make a list of what you need with priorities and just upgrade when an upgrade comes along, it is not so bad. Of course, all missions are easier with the G5 stuff. But almost everything is as doable and fun with G3 or even G2.
As for the scope of what I achieved: In the three weeks or so (maybe it was four weeks, I don't remember) I did settlement missions during EVERY play session, I assembled a G5 Maverick with two additional mods (it came with two installed), a G5 Dominator with three mods (one preinstalled), and one of each G5 with four mods of the shotgun, pistol and sniper rifle. Frankly, the only weapon I ever needed was the Tormentor anyway

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What I am trying to say is what I always say about upgrading and engineering: Just play the game.