I played with map updates and shifting positions from tank to tank as a commander. I don't know the gunnery rating used in the scenario (where do you check that?).
The gunnery rating of your own force depends on your own, personal gunnery rating (we wanted to create an incentive to familiarize yourself with at least one vehicle in SB Pro to the point of being a competent gunner). As you can create several profiles in the Records menu in addition to the rather mediocre Lt. DeFault (with his butterbar-corresponding 60%), your selection of the user profile allows you to control a bit of the balance. I'd say, you should try to achieve at least 80%, beyond that actual balance effects are less prominent.
I don't know how Koen chose the T-72 specific model. I think that it all came out from the North German Plain 85 scenario that I was playing.
Irrespective of the actual tank model - be it T-72M1, or the much better armored T-72B - you can still make a selection for all the ammunition that is modeled in SB Pro and which is suitable for the tank gun with which a vehicle is equipped. Therefore, especially for 125mm and 120mm tank guns there is a pretty wide range of very modern and rather old munitions with dramatic performance shifts.
Do you think the scenario is unbalanced?
I don't think in terms of balance, to be honest. Most game designer pay a lot of attention to it, and for competitive network games where you have three races/classes/... it makes a lot of sense in order to retain a balance between success rate for the player and keeping it challenging.
SB Pro however is a simulation. If a scenario can't be won, well, there's a learning effect in that already. All I'm saying is that depending on the settings, the balances can be tilted in your favor, and that surprisingly few SB players pay attention to it. Instead they always go for the highest difficulty settings. This tilts the reaction speed (and often also the gunnery rating) in all computer vs computer engagements in OpFor's favor. Combine that with ammunition that regularly kills a target with the first shot, it is blindingly obvious that such a combination will be nearly impossible to beat unless there are severe tactical blunders.
Only medium difficulty will give you balanced reaction speeds, and MAYBE an advantage to you with the gunnery rating.
Realism settings do not influence the balance at all, or at best very subtly so to the extent that the lower settings activate certain helper features like marking a spot in the map by lasing it (it'll create a red dot). That can help to eliminate player disorientation at times.
Therefore, tweaking the conditions of the battle will allow you to determine the point at which the balance may shift against the Soviets in this scenario. This time you got essentially overrun. Only if NATO cannot maintain - on average! - a 3:1 exchange ratio in all tactical engagements (which means that you should actually strive for a 5:1 or better ratio in order to make up for those battles of other, weaker commanders somewhere else), classic North German Plain/Cold War Gone Hot scenarios can be won on a strategic scale. Only if you can delay the advance of the Soviets to ports like Bremerhaven for at least seven days can the Reforger convoys reach the battlefield in time to shift the balance of forces to what it needs to defend the freedom of the rest of Europe (Germany of course will always end up being devastated).
So maybe you want to tweak the scenario, and then try again and see what will happen now. Might be an eye opener.
Also, per employment doctrine, Leopards should try to fight from hull-down positions as much as possible. In the planning phase I tend to use the LOS tool "reversed" a lot in order to see from which positions an advancing enemy would be fully exposed. Then I mark the edges of the red zones with waypoints and assign a Defend tactic to them, pointing into the kill zone. You can leave them unconnected. But as soon as you know that enemy is moving into one of these zones you can quickly send your own tanks to these positions which are certainly better suited than a spot randomly chosen under time pressure. You don't have that time when managing a company team sized force in real-time. You need to shift some of those decisions into the planning phase when you still have the time for it.
(With SB Pro PE 2.6 you can (finally) save the results of such a planning phase as a PLN file which you can later pull from the drawer and refine a little, if needed).
Ideally NGP '85 and Steel Beasts would yield similar battle results, but of course NGP quite necessarily has to work with abstractions and certain assumptions, e.g. I doubt that it resolves shots on an individual tank component basis. That's a perfectly valid approach for an operational level type of wargame, I would probably make similar decisions. The point I was trying to make in my rant is that at the micro level you will notice a much higher granularity in combat outcomes. It can be a battle of near annihilation under certain circumstances. Many mission designers try to balance their scenarios to yield Pyrrhic victories - both sides by and large eliminate each other. Rarely it is anything in between, not the least because most people tend to not give up as long as they have means at their disposal to continue the fight. And of course in a single scenario that isn't part of a larger campaign bad decisions to prolong a fight that has already been lost cannot create an adequate incentive to act "sensibly"; a scoring formula usually is not enough deterrence to keep you from throwing everything that you have into the fire. In your case the only metric of success was whether the Soviets would reach Hameln in force, so you still pulled off a victory - when in reality it would have been anything but an unmitigated disaster.