Okay, here's my two cents...
Beerus, when evaluating Goku, concluded that he didn't think his base form was strong enough to take out Frieza. This is speculation, but it sounds like base form Goku never rose above Frieza's maximum power before he started training. And keep in mind Goku didn't train in the months after Buu was defeated because Chi-Chi made him get a job. So, it's safe to assume Super Goku's base power level is set to that of Buu Saga Goku's base power. And we all know SSJ2 Goku was stronger than Dabura AND Gohan, perhaps on the level of SPC, and if he wasn't, then it would be comparable to a 7 or 8 on a scale of 1 to 10, meaning he would be very close to SPC's level if not a tiny bit above it. Now, there's nothing to suggest that without the God Ki Goku got any stronger in Super. Super Saiyan God, Super Saiyan Blue, SSBK, all those are WITH the God Ki. In his base forms, he's as strong as he was in the Buu Saga. And Trunks fought him damn near evenly when he was a Super Saiyan 2; in fact, an argument could even be made that he was overwhelming him, and it was only when Goku went Super Saiyan 3 that Trunks was held back. So, in conclusion, I would say that Future Trunks is so close to the level of SPC that it's inconsequential. Even if he's not stronger than him, on a scale of 1 to 100, he would be within the 90% range, so 4-B is entirely logical.
But that's just my take on it.