Umm, no. Even if you can argue about it theoretically, it doesn't work practically - for example, let's take Fallout 1-2. Stealing gives you infinite experience if you abuse it like hell - does that mean that the most desirable behaviour there is to steal back and forth from everyone?
Your first problem is that you assume that Fallout had a good XP system.
Another big difference is that DX1 awarded you with exp points and cash for fulfilling (or making progress in) mission objectives, and exploring the levels.
And that was already too much. The reward for exploration should be the stuff you find.
One of the things that pissed me off visually in HR (other than the game being soaked in piss) was that most of the areas felt like an adventure playground full of conspicuously-placed cover, endless vents and side passages. Even when the stealth paths were well-done they were still glaring right out at the player, whereas in DX1 places like the VersaLife Building feel like they might actually be real buildings with semi-logical layouts.
I think the difference might have been that DX1 levels were first built as locales while DX:HR ones as collections of paths.
It's just a hunch, though.
Still, you can't deny DX:HR locations feeling more modular.
I mean, what is the reward of gaming? It's not having max level or good gear or all skills maxed out. It's fun. And fun usually doesn't lie in having all of those - usually, once you have all those that's where the fun ends. And, usually, you have to engage in lots of unfun behaviour to gain all those. So what's the point?
The point is that maxing out your XPs allows you to unlock some abilities earlier unlocking additional options or even unique content. For example if you remain undetected throughout the first mission, reaping all the objective, exploration, hacking and non-lethal takedown bonuses, you can have CASIE unlocked by the time you handle the hostage situation - dude's psych profile and all.
It's not just that the game rewards you with XP, it's also the fact that those XPs keep rewarding you with content, at least until all the useful stuff is maxed out. Want to play with several cool guns? You need inventory space -> you need XP. Want to access interesting stuff early or at all? Maybe take over security systems? You need hacking -> you need XP. Want to reach some otherwise unreachable locations? You need augs -> you need XP. Don't want to cut yourself from advantageous routes suiting your playstyle? You need augs -> you need XP. Want to have any use for that heavy rifle? You need recoil-dampening augs -> you need XP.
The min/max approach in HR would be to knockout all enemies, get the ghost bonuses and then come back and kill all of them.
IIRC you don't get XP for killing the unconscious.
by playing a combat approach you get XP every guard you kill. Kill/Knockout no one and you get no XP, so they added those stealth bonus to compensate.
Of course the fact that KO/killing doesn't invalidate stealth bonus makes it fall apart because you don't need compensation if you can get both.
If anything, the "penalty" for getting spotted or leaving any sort of traces (including dead/KO'd/disappeared guards) should be tightened security and heightened alert in subsequent missions.
That's because the shooting part is designed around a cover system, not as an FPS. Everything from Jensen being super fragile (even with armor aug upgrades) to super precise enemies, enormous zoom boost when you aim from cover etc. points to a cover shooter design.
Actually it's fairly interesting if you refrain from using
wallhack cover system. The AI is about developed enough to be fallible and make it viable despite Jensen's fragility (NPCs don't track your position if they can't see you, so not using popamole doesn't equal being shot to pieces).
Admittedly the
way is more cinematic, but it's an easy mode and does get boring fast.
But they aren't, you only need to press the awesome button to perform non-lethal takedowns while you need to press and hold for lethal ones.
This. If anything non-lethal takedowns should be noisier and constrained (for example only working with unalerted people).
Most weapons are powerful and worth investing in in DX but what separates the sniper and dragon tooth from the pack is that they have some uses outside straight combat like destroying cameras, turrets, alarm panels and even most doors (of course, GEP gun does that as well and is even better at it but it's loud as hell).
SR also combines superior range, precision, firepower and ability to mount silencer (something you couldn't do with ordinary pistol).
Overall DX:HR's weapons are much better in all regards but lack of flavor stuff like pepper spray or fire extinguishers.
Sometimes I feel like you're bad at games. HR is perfectly fine ignoring all stealth. The reward for guns blazing is more action and faster completion time. Yes, you get less experience. No, it won't limit you because to succeed at a violent, noisy playthrough you need less skills. /shrug
Actually, you need more skills. Stealth doesn't really need any particular augs, just like you didn't need anything for stealth in the original - just patience and some thinking.
OTOH if you want to fight you benefit from armor upgrades, rebreather (gas grenades and barrels), flash and EMP shielding, inventory extension (for all that guns and ammo), smart vision (cloaked enemies and enemy movement behind cover), typhoon, recoil dampers, weapon stabilization, hacking to get the shit going with berserk turret or robot, extra movement speed, strength aug to use heavy equipment as makeshift shields and throw it at people, battery upgrades since you can't just wait it out in mid combat, etc.
If you want to go full street-sam you need all the augs you can get, even more so if you want to mix stealth and combat. For pure stealth you need almost none.
tl;dr
Garret doesn't need to Robocop.