I think the combat benefits of Hull Restoration is highly dependent on fleet composition, but there are some reasonable fleets that do well with it. I often think of a fleet composition or play style (the two are tightly connected), and then consider what changes to the character's skill selection you could make to make the fleet weaker or stronger. I tend to have a more difficult time considering skills in vacuum, since their effectiveness depends a lot on what they are affecting. I certainly don't dump the skill for end game Ordo hunting if the fleet has been built around it (especially officers), given it might actually be the most optimal combat configuration for that particular fleet.
For example, Coordinated Maneuvers is great for frigates/destroyers/high tech cruisers, but I often have to reconsider when most of my fleet is composed of things like Legions and Onslaughts, whose burn drive and 0-flux speed boosts are unaffected by the +20% speed bonus. Going from base 27.5 to 32.5 speed just doesn't help that much when burn drive pushes you up to 210.
I consider the Technology tree to be a pretty weak choice when I'm not running phase ships, high tech, or automated ships. Your fleet wide combat benefits at that point are Flux Regulation (which only affects base flux stats - which low tech ships are notorious for having very little of), ECM (which late game Ordos pretty much overwhelm with cores in each ship), and Cybernetic Augmentation (+2 Elite skills for officers which can be nice for some ships but others less so).
For example, I've got an ironman save with a low tech capital centric fleet : 2 Onslaught XIV (one player piloted), 2 Legion XIV, 2 Champions, 3 Enforcers XIV, 1 LP Kite (no officer). Logistics train was 6 Ox, 3 Revenants, Prometheus and a spare LP Kite. Interestingly I had no colonies, but did take a Hegemony commission that run. With that commission it was running net positive passive income of ~8000 credits per month and apparently had accumulated 6 million in the bank.
Skills in that save (elite where applicable):
Combat 5: Impact Mitigation, Point Defense, Ballistic Mastery, Target Analysis, Missile Specialization
Leadership 5: Tactical Drills, Crew Training, Carrier Group, Officer Training, Best of the Best
Industry 5: Bulk Transport, Ordinance Expertise, Polarized Armor, Containment Procedures, Hull Restoration
I probably should have retrained for Field Repairs but hadn't spent a story point to retrain at all.
Officers were seven level 6s and one level 7 (in a Champion) tailored to ships. For example, Onslaught XIV officer was Elite Impact Mitigation, Target Analysis, Ballistic Mastery, Missile Specialization, Elite Ordinance Expertise, Polarized Armor. Level 7 Champion officer was Elite Helmsmanship, Elite Impact Mitigation, Target Analysis, Elite Ballistic Mastery, Systems Expertise, Elite Missile Specialization, and Elite Energy Weapon Mastery.
I'd be interested in knowing how people would change skill picks away from the Hull Restoration + Best of the Best combination to improve that particular fleet's performance for Ordo hunting, keeping in mind that it's an ironman save without any colonies. Assume it's okay to hire and train up new officers with difference skills and spend the 24 story points to do so (presumably you're Ordo hunting for a reason, and without colonies, training up new officers is about all one has to spend points on).
Since I was piloting an Onslaught, Ordinance Expertise is basically required on the character, and provides about 400 flux dissipation and 4000 capacity. Compare that to Flux Regulation's 390 flux dissipation and 9,000 flux capacity spread over all the ships in that particular fleet. Elite Polarized Amor is only a little farther behind the Ordinance Expertise benefit with the +25% vent speed. So I can't really see going lower than Industry 2 or 3. I'm running quad reapers on the player Onslaught, so having a refire rate on them of ~10 seconds with Missile Specialization is quite nice, given you can refire within the overload duration from the previous salvo on a capital, so I'm hard pressed to think of some combination that helps more than Combat 5 as well.
Splitting between the Industry and Tech trees still requires taking a total of 2 campaign layer skills which doesn't actually reduce the number of campaign layer skills taken. Also Navigation is kind of weak given the fleet already has a non-sustained burn speed of 13. Gunnery Implants is nice, but not really required on a player piloted capital with ITU, Ballistic Mastery and burn drive. The AI needs the extra range more than an aggressive human pilot.
I'd also be interested if players were restricted from using save/reload to go back in game time but only used it save after a play session (i.e. ironman mode), does the value of the skill go up?
As for some of the ideas for allowing you to do a restoration away from a dock, I will point out if you are at the point where credits are of no concern and removing d-mods is only spending money, you can bring along a couple Starliners, and drop a colony on a nearby planet, restore all, and then abandon the colony. 2 Starliners will let you do that 3+ times. Or even leave it there for awhile if farming Ordos in a system. You'd want to do that anyways if you're using a Ziggurat to farm Ordos to get back to 100% CR instantly. Virtually any system where you are going to be fighting a lot has a planet you can do that at.
In regards to Derelict Operations, it's most powerful when combined with Support Doctrine and you spam ships that don't care about line of sight, specifically carriers and missile ships. Spammed Moras is the classic meme (3 wings and 2 harpoon missile pods is kinda crazy for 11 DP), but you can augment that with Legion XIVs (22 DP but got to find them), Gryphons (11 DP) and Condors (6 DP for 2 wings and a missile pod).
Both of Industry's tier 5 really need the Leadership capstones to give their best performance due to stacking or synergy.
Overall, assuming Ordinance Expertise and Polarized Armor maintain their strength for low tech ships, I think Hull Restoration is in a reasonable place. It's effectively +1 non-elite skill (i.e. Combat Endurance) to your whole fleet (without DP limitations). I kind of view an s-mod as approximately +1 skill as well - hardened shields vs Field Modulation, Impact Mitigation vs Heavy Armor, Helmsmanship vs Auxilliary Thrusters, etc. So in my mind the combat benefits of Hull Restoration is on par with that of Best of the Best, at least when combined. The campaign benefit is crazy good compared to nearly anything else on the campaign layer.
However, I will say if Ordinance Expertise gets nerfed in the next release, then I would definitely want to see combat buffs elsewhere in the Industry tree.