I gave the low to mid tier mercs another shot and tried restricting myself to no high tier mercs on my current playthrough and it's mostly ok if I don't fight any tier 5 bounties except that I still find that anyone with less than 150 health gets taken down unacceptably often unless you save scum or restrict yourself to only fights where nothing has better than a rifle. I'm running with Bud, Dexter, Doyle, and Aiko.This is true, i simply don't do top tier bounties at that stage. I'm not a speed runnier myself so i don't enjoy and thus do not pursue the idea of being able to do everything and be done with everything within a month or so. So i simply follow a casual path and bother with stuff much later on if it isn't convenient to do so earlier. I have no problem running around without a single slave for months for example.
From what I've noticed, a plasma gun crit can 1 shot someone with 75-100 health in anything less than duraplate. With duraplate someone with 75 health can still be taken down with 2 crits by anything stronger than a rifle and 3 with a rifle. So unless everyone has at least 150 health you pretty much have to be able to guarantee that no difficult fight ever lasts longer than 2 rounds or you're going to be losing people. Melee is a bit wierd since it seems like it can crit for high damage even against decent armor but frequently does almost nothing if not a crit.
I will say that I was pleasantly surprised by Bud in my current playthrough. I made sure to grab him on day 2, max out his attention whore thing and keep it maxed, and he critted his way to 70 aim in slightly over a month with zero training. That is WAY better progress than I've ever seen from him before. I think if you start with a combat build and actually train him up to more like 80 right away he could actually get to where he can use something better than a rifle within a reasonable time. The problem is he still only has 75 health.
I think the idea of building up the low to mid tier mercs would be interesting if there was a way to boost their health, but otherwise I can't really see it being viable unless you have at least 3-4 people using plasma guns, which means you're paying for ammo on all but 1 of them. Bud and Dexter could make an interesting long term option if you could convince Dexter to get rid of that pistol.
Personally, I think we need a way to train health by 25 points twice on all of the mercs. I would offset that by reducing health by maybe 25 pts on Doyle and the top tiers. So they'd start at 125 but you could eventually boost them to 175. The more interesting option to me though would be that you could then boost Dexter to 150, the 75 health mercs to 125, and even get Rifle Savant up to 75 if you wanted. That would make the low to mid tiers MUCH more interesting as a mid to long term option. Implants for mercs would be another option.