Extremely well, honestly. Comparing GT and Super is difficult, so I can't make a call on how he'd go against someone like Jiren, but he's definitely stronger than 99% of the competition.
Interview was recently read stating that Goku was holding back in his Blue form. The only reason he transformed was to motivate the people he is fighting. He's basically holding back and isn't even fighting serious. Well, not yet.
To some, no. To me and you, yes. A lot of people here thought Goku was going for the kill against Krillin. The interview was primarily in reference to his fight against Kale.
Never let anyone else define you. Don't be a jerk just to be a jerk, but if you are expressing your true inner feelings and beliefs, or at least trying to express that inner child, and everyone gets pissed off about it, never NEVER apologize for it. Let them think what they want, let them define you in their narrow little minds while they suppress every last piece of them just to keep a friend that never liked them for themselves in the first place.
Be that as it may, the mechanics of Goku's [single] universal feat are hardly any less suspect. When asked recently on twitter if the current Goku could destroy the universe, one of the writers for Super answered "Maybe if he became a God of Destruction. But even if he could, he wouldn't do it."
This is consistent with the series only alluding to the destruction of the universe where the Gods of Destruction or Zen-Oh are involved, which leads me to suspect that the expanding energy waves from Battle of the Gods were related to the nature of the Energy of Destruction Beerus possesses as a GoD rather than the force of their punches. If that really is the case, then it's not really that unlike the situation with Omega Shenron's negative energy.
But, if you want to go on thinking that training for a couple months made Frieza strong enough to punch the universe away, that's your prerogative. Makes you wonder why people are so afraid of Zen-Oh if it's that easy, though.