Too bad there's no real reason to play low AR since. It will just become a "look I can play all AR's" (look at me!) feeling, if you do accomplish it.
Practically everyone can play low AR, while not everyone can play high AR. The mods are there to increase the difficulty, otherwise it is a battle of the SS's. Although getting less than an SS is not a true reflection of your rhythm accuracy either, neither is an SS.
The people who can only play high AR chose to do so because of the competitive nature of the game. If the scoring system were different, they would know both... because it's at a point where every map needs to be played at AR9.6+ to get a rank.
The "pro level" (ugh) is the point where osu! stops being a rhythm game. Until then it's a rhythm game. To be the best from there onwards, it's all about improving your [reading/aim/speed] and [reactions/anticipation/memorisation]. But you need a decent amount of skill in rhythm first. It's just that those other skills will improve much much more, and rhythm takes the back seat. If you get worse accuracy on really hard maps, it's not exclusively because your accuracy/rhythm sucks, it's because those other skills suck, and naturally affect it.
Learning low AR will toss out the second skill bracket, and place new rules on the first one, which naturally changes all aspects of/and puts more weight on reading, putting the handbrakes on your aim and speed. It is actually quite a huge change and this is why, in other rhythm games, AR is customisable and players usually settle on 1 speed or a small range of speeds, forever. In osu!, that is currently AR9 - AR10.3, forced on you by the game for rankwhoring reasons.
So before you think about learning the "lesser skills" - ask yourself... Dafuq am I doing this for?
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