Wow, some have trouble accepting reality...
If the "personal loot pool" loot system actually existed, THAT would have been gambling!
It's not a component of randomness that defines something as gambling, but the complete lack of influence over the outcome! Emphasis on complete lack of influence. A slot machine that pays out 90%, but in a non-random way, would've still been gambling, it would just been easier to catch on that you actually have no influence over the result.
So, if you play a game where you can't influence the outcome, that's called gambling, Roulette, slot machines, lottery - all pure gambling. If you can influence the outcome a little, though, it's a little different from gambling. If you can SIGNIFICANTLY influence the outcome, then it is SIGNIFICANTLY different from gambling! If EU isn't significantly different from gambling to you, then it's because you're playing it like it was a slot machine, just pulling the lever and IGNORING all the aspects of influence where you could've improved your efficiency (probably bashing all who told you eco matters). Yeah, you probably subscribed to the "personal loot pool" myth because it made the losses seem not lost, but remembered, so you could continue hoping for the big one, believing everybody gets the abysmal 90% TT back, no matter what. Nothing new here, all gamblers subscribe to this kinds of myths - it's simply a rationalization for their losses.
Just like a slot machine guarantees you a fixed long-term X% return rate if you keep pulling the lever, a "personal loot pool" would guarantee you a fixed long-term return rate, let's say 90%, regardless of how you "pull the lever". Using eco or non-eco gear, you'd get 90%. You'd shoot in the air, you'd get 90% - eventually, when you'd decide to actually kill something, of course. That would've been a ridiculous system, completely eliminating the importance of any skills, not to mention how inefficient it would've been from a technical viewpoint (would require tracking historical expenditure for an effect that amounts to what a slot machine achieves without memory).
Compared to the "personal loot pool" nonsense, the actual loot system where loot is scaled, primarily, by the total inflicted damage, is definitely not gambling. In such a system it actually matters that you inflict damage at the lowest cost possible, which, then, directly translates into higher return rate (return divided by cost) for you, the smarter player (you didn't expect to do good playing dumb, or did you?). If you shoot in the air, you obviously inflict less total or no damage, hence less or no return at all. If you use less eco gear, your return rate will be less, since your cost is higher, also. And it's super easy and efficient to implement, since it's basically reduced to picking a random value from a predefined distribution and scaling it by total damage inflicted. No need to review and track historical expenditure at all. The key thing here is how much you buy the damage for. Obviously, the lower, the better.
Since EU gets compared to a casino a lot, let's make sure the analogy is accurate. If EU was a casino, let's say a slot machine, then it's a slot machine where the cost of a lever pull is not fixed, but variable. How much you pay for pulling the lever is largely up to you, whereas in a casino it is not, because the price is fixed - hence, it's pure gambling. I'm not even going to go into the fact that what you loot in the EU style "slot machine" can be cashed in for variable amount of money, where you, again, have some significant influence. Of course, the EU "casino" has an additional risk of increasing average player efficiency (compared to an actual casino, where the return rate is fixed and can't change). Hence, the adjustments (which, probably, reduce to the adjustment of the average TT return rate in a way that keeps EU operating at a positive cash flow).
So, in summary, "personal loot pool" would give you a fixed return rate, no matter what - compared to the actual loot system, that actually rewards efficiency. The "personal loot pool" would obviously have been pure gambling, with no influence over your "personal" outcome. On the other hand, the actual system gives you quite a lot of influence over the outcome. Just compare damage/pec for various weapons, think of all the gear combinations you're able to use against a certain mob (efficient vs non-efficient armor, healing tools and weapons), think of all the play styles that can be used with varying costs (e.g. 10% overkill vs 2% overkill, tanking mobs mobs 100% of the time, while you could've avoided half of the hits and reduced defensive cost to 50%, etc), etc.
No, IT'S NOT GAMBLING and it never was. But, seems people who like to pull levers with a fixed return rate would have liked it.