Is it really though? There are some really good active protection systems like Israel's TROPHY which do a pretty good job taking out incoming sabot style (tank shell, javelin, RPG) warheads. The modern incarnation[1] (M1A2 SEPv2) of the US Abrams tanks all have it
A sabot round is really two parts, right? You have the shaped charge that blows up exterior armor and then a small penetrator, generally the size and shape roughly of a pencil, that goes in and makes a tiny hole.
Active protection systems like Trophy are designed to pre-detonate that shaped charge so that they actual sabot penetrator just bounces off the normal armor, or is hit by ERA (explosive reactive armor). I'm sure APS work better against most ATGMs than sabots, but fundamentally, many of them are designed similarly. Sans maybe there are no depleted uranium ATGMs.
modern APFSDS rounds work purely through kinetic energy penetration and don't contain any explosive charge. The penetrator is usually around an inch in diameter, and maybe 30 inches long. I doubt Trophy can target these rounds effectively since velocity is just too high, something like mach 5 (compared to a javelin's paltry 140 m/s).
A TROPHY system wouldn't screw up the APFSDS round's bearing and structural stability? I know it's moving really fast, but how effective is it should the tip be broken off, or the round begin to tumble in flight before hitting the tank at a broadside angle?
IF the APS system (Trophy or Arena) could hit the sabot in time, yes, it would diminish its penetration capability substantially. Whether it can react fast enough to do so is doubtful. 3500mph projectiles are tough to counter. There have been plans to try to deflect it via armor so the tip gets shattered and the energy dissipated, but I'm not sure how effective that is with current armor tech.
The US latency target for APS from detection to engagement is tens of milliseconds. That is good enough for just about everything except sabot from short range.
I said sabot style… meaning explosive shaped charge to take out external armor, and usually a small (usually titanium) penetrator. An RPG just has the shaped charge aspect. Trophy was designed exactly to kill stuff like rpgs.
I also should have been clearer, there are other options. The Brits like this idea of HESH. This works against both tank armor (though less than APFSDS rounds) and fortifications alike. This way the tanks can carry just one type of armor instead o f having to manage a mix. HESH has persisted because the Brits like rifled barrels, and doing a sabot round with a rifled barrel has proven quite difficult.