Ok, this seems like a mathematically proven concept, and thats the answer I am searching for.
Thanks a lot of for explanation, it helped a lot. Can you please ask him for the following?
Pot is 12bb, lets say you overfold and he wins 1.5bb from cbetting (that's a lot), so his 3bet bluff+cbet is -3.5bb total for him
This is based on that all my bluffs from preflop are super rarely flopping medium hands or strong hands or profitable bluffs postflop. Or in other words my preflop bluffs stay bluffs postflop so EV is based purely on bluff bet on flop.
So we can calculate EV of bluffs preflop
EV = p_strong * EV_strong + p_draw * EV_draw + p_pure_bluff * EV_pure_bluff
Here, p_pure_bluff is the probability of having pure bluff on flop, and probabilities sum to 1. So you only considered here EV_pure_bluff, and ignored first 2 terms when we hit strong or draw (weak pair is also draw).
So, even with worst bluffs like 27o I will sometimes hit strong hand, and sometimes hit pair which can get IP to showdown. So i think that 1.5bb is actually very underestimated. It is true that so weak bluffs rarely flop good, but why would I use so unplayable hands vs someone who I expect to rarely or never fold vs my preflop small size 3bet?
For example, I would rather use in BB vs SB or BU vs CO hands like 57s, 68s, K9s, Q9s, as bluffs which flop reasonable often strong hand or profitable bluff. And yes if I make my range depolarized, you can 4bet, but I can also min 5bet then you have to shove, so 4bet is not a solution for you when you defend 100% range, you still need to call OOP most of your range.
So this argument, that my bluffs will be -EV if even if you overfold flop, is similar to argument for cold calling open raise e.g. BU vs CO. I risk when I call CO 2.5BB, and if CO checks flop and overfolds, and I win with my bet 1.5bb, i still lose money because i invested 2.5bb preflop. Thats why I need to cold call only hands which often enough flop either good hand or profitable enough bluff.
So, I can use for "bluffs" 3bet exactly the hands I would use for cold calling which will total play +EV for the whole hand (if it plays +EV when I cold call, it will be even higher EV when I min 3bet and you defend by calling because you will overfold + you will have cappt range and I will not).
So my 3bet range would be the value part 99+, AJ+ together with all other hands that I would cold call vs CO open raise, so with this all my hands should be +EV. In that case, my 3bet range would be vs CO around 15%, from which I can easily defend vs 4bets by having min 5bet/fold and 5bet/call range, together with 4bet call range. So with 4bets you will have value with premiums, but you have to defend 100% range, so premiums is only small % of your range.
What I find as big disadvantage of 3betting small is that because of incredible pot odds that villain gets, I have to give up on flop very small % of range comparing to 3betting standard, which is harder to achieve with balanced range. So I have to make sure that I don't give up too much on flop so that really each call 3bet is +EV for you.