I was looking for a bit of extra difficulty and I thought this would mesh well with your other combat mods. Unfortunately the biters become completely oppressive and I was spending far too much time dealing with them. Aside from sniper turrets which might be worth the logistical upkeep, the other ammo turrets also require similar upkeep but also have insane costs (including alien artifacts, which with a clip size of 4 on some may be too expensive to run). Cat 5 biters instagib bots, the acid puddles are instant death to step on, among other problems, and their resistance to lasers is extremely oppressive.

Some of this may be due to also playing with Space Exploration which also locks the higher tier damage techs behind much more complicated science pack recipes, slowing progress, but I think the spitter puddles and instagibbed bots would continue to be a problem. Even with Alien Loot installed (on default settings), I don't see how a defense setup would be remotely profitable given how much loot it would take to replace a destroyed construction bot given how often they die.

Just thought I'd give some feedback given my experience with a few dozen hours fighting cat5 biters and having a taste of the cat6.

I have designed things to work in some way (assumably only my mod suite without external weaponry mods' help), but was afraid of "guiding" players, taking away the fun. But as you faced difficulty, I will give out some hints to help you a bit.

1. Use stasis beam turrets and force cannon turrets to support your DPS-dealing turrets. They will buy a lot of time for your defenses. I introduced them for a good reason, not as useless cosmetics.
2. For all clips by Schall Alien Tech, it is NOT always the best to use the best ammo (Refined ammo) everywhere, because of diminishing return in terms of the cost of alien artifact. For the same amount of alien artifact as ingredients, the total damage output is 4 : 2.5 : 1 for standard : condensed : refined. Reserve the refined ammo for what you feel critical or suiting your taste, such as the longer freeze time of stasis beam or large AoE area of BFG.
3. Yes, I intentionally nerfed lasers on my high tier aliens, because vanilla laser turrets are just too good (both range and damage). Vanilla players tend to overuse and spam laser turrets everywhere, and do not care about other damage methods. My intention of creating several enemy/weaponry mods is to change this "boring" behaviour. So players have to mix various types of turrets in order to stop the aliens. In my set of mods, Category V (or larger) aliens would be dealt with sniper turret, cannon turret, particle cannon (BFG) turret with the help of stasis beam / force cannon. Laser turrets remain useful against the ordinary (vanilla) aliens.
4. If you find the loot to few to support research/ammo uses, there are various mod options adjusting the "richness" of the loots. I created these options for players to adjust their own difficulties.
5. I have also created two mods for loots pickup. Schall Pickup Tower introduces radar-like entity which "auto" collects any nearby items on ground. Schall Remains & Pickup gives a new hotkey so player can "manually" collect items around over a large area. Therefore, bots are longer needed to go beyond defense line. In my games, I used belts/loaders/long inserters to feed ammo, so only need bots for repairing (sometimes).

To clarify, the challenge was manageable in most ways, but introduced more frustration than gameplay value in my opinion.

1. These turrets use ammo. For maintaining several kilometers of walls, this is a huge additional logistical challenge. I wanted some challenge, but I found this aspect overwhelming when my current game requires that I capture so much territory.
   1.2. Ammo requires alien artifacts, so collecting and returning the loot requires extra overhead.
2. Even the first tier of ammo clips used 5 alien artifacts per. For a particle cannon for example, it has to get roughly 2 kills per shot to break even on ammo. This isn't including other losses due to repair packs and bots.
3. Lasers have a large number of advantages. It's okay to nerf them so long as other options are viable and match the additional logistic requirements. For my particular game, cannon turrets were not viable because of oil/plastic needs and sniper turrets were more than sufficient, but I generally had better success with scheduled artillery "maintenance" to keep biter threat down.
   4 and 5. I see the options for boosting and collecting loot and I did make use of the pickup tower in some locations. The clutter of loot is a bit bothersome and I had been considering some alternative design choices, like a long range radar that collects loot from it's scanned chunk, equipment that greatly improves a vehicle's pickup radius, or dead aliens spawning or incrementing a resource patch. These options would make the extra clutter of higher loot drops less bothersome

When you say you need so much ammo (thus ingredients) to kill, I think your lag in related damage upgrade tech (as mentioned in your first post) is really a lot. In my games, I used mix of most turrets on defense, and there are a bit excess of alien artifacts (default loot settings) for damage upgrade research, which in turn conserves ammo.
Some other players (non-SE players) even commented too much loots then what they needed, and asked me the way to reduce loots a bit...

My mods are all designed to be balanced with vanilla game, but not any overhaul mods (including SE) that may change things a lot. SE may have changed tech tree related to vanilla rocket / space science more than I have imagined.
Anyway, from comments about SE (including yours), I feel SE has nerfed production of space science packs, limiting normal damage upgrade research, thus hurting a lot in the effectiveness of my particle weapon system in Schall Alien Tech. I guess this is the ultimate reason why you find the turrets/weapons are underpowered. Expensive ammo cost (& etc) are just results after this.