From what I can tell, you want to use a polarized 3 betting range in earlier positions, and a linear 3 betting range in later positions. The reason behind this is because it's easier to realize your equity in late position so 3betting with your entire continuing range at some frequency is less risky OTB vs like MP1.

Is this correct so far?

That leaves me wondering, at what frequency should we be 3betting our entire range? The polarized 3bet is much more clear, cause you can pretty much always 3bet the top and bottom of your range and be ok.

I recommend a polarized 3b range when you have position on the opener, because they will most likely 4-bet or fold, but a linear range when you are OOP to the opener (e.g. in SB v BTN), because the player in position will do a lot of flatting, so you need some actual post-flop equity/playability if you 3-bet when OOP.

e.g. On the button, you can 3-bet 76s as a bluff, but call with mid-strength hands like TT/99. In the SB, you generally 3-bet hands like 99 as part of a linear range, and have almost no flatting range.

EDIT, to put it another way:
When you're in position you have 3 groups of hands. "Value 3-bets" like AA, mid-strength flats (AJs, 99), and "3-bet bluffs" like A5s, 76s.
When you're OOP, you only have 2 groups. To balance your "value 3-bets" (AA etc), you use the mid-strength hands (AJs and 99 become 3b/folds), and you just fold the worst hands (76s etc) as the latter aren't profitable OOP.
In short: The polar range is top and bottom of the 3 parts of all playable hands. The linear range is top and middle.

A lot is player dependent. If someone always 4bets or folds turning a value hand like qjs into a 3bet/fold is a waste, so polarized makes sense.
If someone always calls your 3bets, seeing a flop with K4s and 42o is not going to play well, so 3betting linear for value and postflop playability is far more optimal.

I think what your saying is IF you have to 3 bet 30 or 40 bucks in a 1/2 NL cash game only to fold it to a 4 bet You are probably better off sticking around to see the flop even OP ?
IMO I have found that in most 1/2 cash games guys IN Position who just 3 bet you are not folding to your 4 bet unless your 4 bet is fairly sizeable and if they do call a sizeable 4 bet they are probably sitting on a very premium hand.

When someone opens from whatever position, they hold a range of hands that offers the opportunity for opponents to gain ev by playing profitable hands either as a call or a 3+ bet. The correct 3 bet range vs a defined opening range then carries an innate amount of ev. Changes in this ev can occur due to opponents tendencies, your own weaknesses and strengths, or the other players that have yet to act.

Drawing hands that earn very little ev as the 0ev margin is approached near the bottom of the 3bet range are the most vulnerable to these ev shifts.

The hands near the (call/3bet) margin are much less vulnerable to these ev shifts.

Notice that I haven’t mentioned the opponents fold/call/4bet frequency yet. This is because default strategy vs a given range should be decided first, and then adjustments may be made on the margins depending on these frequencies.

These adjustments occur on both the fold/call margin and the call/3bet margin.

For example I 3bet hands as weak as 76s(btn vs co 2x) as default. I might fold this hand vs a player that 4bets a lot and denies equity effectively post flop. Or vs a player that never 4bets(a significant loss of value) I would expand my 3 bet range beyond 76s.

The call/3bet margin is defined as a positive ev region containing hands that earn a significant portion of the pot. These hands make many strong hands postflop(the primary ev source in the game of poker) and if the default strategy has been correctly constructed depending on the opponents opening range, there is no need to make drastic adjustments on the call/3bet margin.

For example if I think QJs is a slam dunk 3bet vs the 2x co opening raise(I do) then no opponent deviation will cause me to fold nor call. There’s just so much ev built into the hand in that situation given a strong opening range for the opponent. Only thing that could change my mind is a change in the opening range itself.