It is not, GLATGM are nothing else but ATGM, they are constantly used within 2km range and at any distances ATGM retain their lethality.
In agree in part, but GLATGMs are in fact 'limited' ATGMs. Kornet is 152mm in diameter so can easily get to about 1200mm+ RHA performance - whereas Reflex with its 125mm is limited to about 900mm RHA - which is probably struggling against M1A2 frontally. Thing is, late model T-90s and late model M1s probably will have difficulties killing each other from frontal 40° above 1km or so (neglecting lucky shots or damage to sensors etc.),
Lets take the maximum engagement range of 5 km for the sake of argument, both tanks would indeed struggle to penetrate the actual armor frontally as you said, however the objective is not to penetrate the armor and kill all occupants, it is to neutralize the threat of enemies tank forces. This objective to neutralize enemies tank forces can be provided by mobility,firepower kill or comprimizing their capability and certainly T-90 has still higher advantage due GLATGM to achieve those things, before it gets even remotley into effective range of M1A2 tank, not to mention it lacks adequate firepower to deal the same damage in return. It lacks proper ammunition to fullfil this gap of maximum range engagements.
and due to seperate loading ammunition and limits on APFSDS-penetrator lenght T-90 might even be at a slight disadvantage in a direct duel (also, current RA loadouts still seem dominated by relatively old BM-xx rounds, even if better prototypes and models exist, whereas the M829A3 is fielded in numbers)
It is limited however the T-90A was upgraded to accomodate longer APFSDS, not equal in size of M829A3 but still it has increased its capability, but that is besides the point unlike Abrams the Vladimir posses very potent Tandem HEAT rounds and it makes no difference how underrated such rounds are in the West due the lack of interest the Americans show, reality provides far better solutions by other countries and the US always lacked there.
The M829A3 exists in very rare numbers according to Fofanov and others. The standard round is still M829A2.
So, GLATGMs are nice to have, but in a direct confrontation with M1s they probably don't bring that much to the table (besides, such comparisons are mostly pointless, there are no "neutral" environments one can pit tank X vs tank Y)
A good commander chooses his battlefields whenever he can, giving the fact that Russia will always be the defender not the attacker it gives them the upper hand for such scenarios and self dug up tank defences will certainly help for lower visibility, protection and therefore maybe even a surprise attack, but that all is merely a speculation without having actual circumstances of events to evaluade such "duels". That won't matter much since Duels are unfavored and biggest threat are ATGM teams and they through time have shown more firepower than tanks provide in protection along with the longer arm of warfare.
EDIT toa add: you're right of course that KE won't do much good against non-tank targets, and indeed there the US has long lagged behind in that terrain (with 120mm HE rounds only recently and due to experience IN the ME being developped and fielded). But that has little to do with a T-90 / M1 confrontation.
Well and that is often the most wrong approach of evaluading technologies and their capabilities. See that often when people try to compare Attack Helicopters with each other, lot of people seem to want compare them in a "dog fight" rather their capabilities for intended role and for circumstances of providing CAS under enemy prescents of AD systems. Same i compare for tanks, they will engage 20 ATGM, RPG, Mortar equipped infantry before they will engage in a Tank duel, so their capabilities to deal with such high occuring threats is important.