Penalty on the play! If you're not factoring in hit rate, you can't do any sort of any real DPR comparisons with GWM or SS.
Ok, but then you would also need to factor in crits too and the bonus action attack that comes with a crit or a down.
Bottom line, GWM is going to give him an extra attack every 10 turns plus every time he downs someone and because he has a higher damage weapon he is doing more damage on every attack and on every crit even he never takes the +10 damage.
At any armor class he is going to more damage than a "normal" bladesinger while also having high spell attack rolls and spell save DCs.
They also do not get a fighting style, have d8 hitpoints and do not get extra attack until a level later. Extra attack costs an invocation on a Warlock. A Warlock can only do this with 1 weapon at a time and that weapon can't be a 2-handed weapon. A Monk also allows non-finnesse weapons with dex, but likewise it is only simple weapons and one other weapon that can't be heavy.Now, obviously opening non-Str stats for GWM is nice, but it's not novel; hexblade and battle smith already allow this. The point of the query I asked is a feat enough of a cost to allow it.
IMO, it is WAY, WAY OP for a feat.
No not all to make a different stat slightly higher, you would do this for the ability to completely dump strength on a heavy weapon melee build. And it is not "at least" level 8. A fighter can max his ability at 6th level and he can even do it with a half feat at that level.But it costs a feat. A feat is a big deal! You're going to be behind a +1 to hit and damage until level 8 at the earliest, or you're going to spend your level 1 Human/CO feat instead of grabbing a big feat like GWM or Lucky or PAM. All to make a different stat slightly higher. Not to mention you still need decent Str or Dex for your armor.
As you have said, the whole point is to make your character SAD. If you need to run a 17+ strength for armor then you aren't SAD. If that is the case why not go to 8 strength and wear medium armor? There is no reason at all for anything higher than 8, it is a waste of point buy.
The ability to spread 9 points around to your other abilities in point buy is far better than GWM, PAM, or Lucky. Statistically it is better than all three of them combined as they cost 2 ability points each when taken as an ASI. You will be better at fully 17 of 18 skills and better at the 5 most important saveing throws.
At level 1-7 (or 1-5 for a fighter) you are 1 point behind in attack rolls and damage with weapons and an average of a point ahead on just about every other thing you do. Above level 8/6 you are not behind at all on attack and damage, but you are still ahead at all those other things.
If you want to make it a feat here is something that is a bit more balanced:I'm not really worried about this for my group. I'm just curious what people think the theoretical cost should be to make a character SAD. Most people seem to think a level 1 hexblade is too cheap a cost, so I'm trying to figure out the general consensus as to the right price.
Zen Weapon - You have trained to use your mind to fight with a specific weapon. Raise Intelligence, Wisdom or Charisma by 1 point and pick one simple or martial weapon which does not have the Two-handed or special property. You get proficiency in that weapon if you don't already have it and can use the ability you increased for attack and damage rolls with that weapon.
This is much more balanced IMO. It makes the use very narrow (1 weapon only), it is similar to the Monk and Warlock ability that limits it so it can't be chained with things like PAM or GWM and eliminates the highest damaging weapons.