The GTO answer is yes it is exploitable as you are not perfectly balanced one could learn your exact strategy and deploy a counter strategy that makes uses of the unbalance in your 3 bets. e.g. not enough coverage on low cards could mean that calling your 3 bet with 56s becomes profitable from IP as that kind of cards hit a low card flop extremely well.
And indeed having a weak calling range is def exploitable as it lacks coverage on broadway cards.

The human answer well that does not matter as no one will notice until you play like > 200NL :)

You can have a linear with polarized elements =D they are not mutually exclusive.

I use to/still am stressing over BB 3bet ranges, so many people say different things.. at the end of the day TBH i think just having a solid frequency is what matters. so BB vs BTN, as long as you 3bet 15%~ and not with ridiculous hands thats gonna be okay.

Having different hands and "coverage" in both your calling and 3betting range IMO matters more vs

1.Stronger thinking players that will take the step to actually exploit you, Ex. If i know someone always 3bets AQo AQs BB vs BTN, when the board is something like AQ2r KJTr Ill just go ham. Some players wont do this though, so it doesnt matter! =D

2.In a consistent pool where people can datamine you. if you play anonymous, or switch around sites often, blah blah, its extremely hard for someone to figure out your exact 3betting range. How are they gonna know?

Also, you dont need to flat strong hands preflop to have strong hands postflop. Sure, some flops will be unfavourable for you like AK2, T92r, K72r, etc, but you will have some flops that are favourable for you, like 654r, etc.

Linear range = topheavy raising range (i.e. TT+ raise, 22-99 call)
Polar range = top- and bottom raising range (i.e. QQ+ and 22-44 = raise, 55 - JJ = call)
Mixed range = combos get raised or called (or folded) at certain frequencies (i.e. KK+ = 80% raise, 20% call, TT-QQ = 60%/40% etc.)

Linear and polarized ranges can get mixed, where the strongest hands regularly get mixed between raise / call and the lowest hands get mixed between call / fold.

Just to get the terms clear. :)

BigFiszh