Three things to take into consideration to construct default-ranges: Gap Concept and Indifference Principle.
Gap Concept: Old concept from David Sklansky:
"You need a stronger hand to call a raise then you do to make an opening raise."This concept is pretty simple and no one give a fuck about, because it sounds to easy (for most regulars pokerstrategy only makes sense if it is advanced or complicated, simple strategy "lol") but try it, if you constantly violate the concept all hands you call "wrong" you'll play -EV in the long run.
Domination (a bit like Gap-Concept):
A hand like T9s is not a huge +EV call, it is +EV to call but not great, because CO has a lot of combos Tx (offsuit) which dominate our TPs (the weakest offsuit 9x is A9o) and all 16 combos AT to dominate our TP and non-nutstraight. If you 3bet instead, you'll make all these better hands fold and have a hand which can flop high equity and make better hands fold postflop (nice bluff barrel hand which makes straight were villain often has sets or twopair).
Indifference Principle:
There is an optimal openraising strategy for the CO out there, no one knows the correct frequency and range (so it is very theoretical now but good to make approximations) and the job of the BU SB and BB (all toghether) is to make the weakest hands in the CO openraise range indifferent between openraise and fold, they do that with a certain frequency of 3betting and calling. The weakest hands to openraise profitable are something like 97s, A8o, J9o. They do that by 3betting and calling but you have to look at the range to find good approximations.
Now the BTN:
A call on the button is not very attractive unless the blinds are passive/fishy, because of bad direct pot odds and a lot of hands have simply a higher EV in 3betting than in calling because 3bets are the death for the weakest hands in the CO range, because they have to fold and have no chance to realize equity. Furthermore the blinds have a very good spot to squeeze and the COs best choice is to defend by 4betting against squeezes not call because of the bad relative position. Bad for calls.
Another point of view: a 3bet sucks for most of the hands in the range of the CO and against 4bets we have position and can defend accordingly well with calls.
If we sum these arguments up, we have to be careful tight with our default-callrange against CO openraises. AQs and AJs are good hands because we keep the offsuit Jx Ax Qx which we dominate in Villains range and have hands that can stand squeezes. AQo the same imo. Same for mid pockets 55-99, the rest is close and often better to 3bet instead of calling. Some suited broadways are also good to call because they dominate suited connectors which may fold against 3bets (the CO can fold a lot against BU 3bets).
It is not GTO (or maxEV) but a good strategy in my opinion: 3bet only with a linear range should work well and is easier to play against CO from BTN.
I only widen up my call range if there is a fish in the blinds (hands which makes good TP), if the blinds are nitty I 3bet more if CO folds a lot against 3bets and call more if he is simply bad postflop (stat-based play but dont overuse it
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---> offsuit broadways weaker KQo are not close, just crap imo.