[spoiler] The reasons why future Gohan is so weak
I've seen a lot of people complain about future Gohan not being strong enough to beat the androids despite having 13 years to train, and I wanted to explain that:
Gohan and the others didn't know about the androids arrival, so ChiChi probably made him study and slack off, and while the androids murdered everyone he was probably around as strong as 2nd form Freeza
As a child, he had seen everyone get murdered, so of course he would fall into despair and be too scared to even train for the fight with androids
Even if he did want to train, he had not a single character to train him (aside from Korin and maybe Roshi, but it's not confirmed he's alive in the timeline, whose training methods wouldn't be really effective to him). He didn't even have a sparing partner for most of the time since Trunks was a little baby (yeah, Gohan was a kid during saiyan and namek saga too, but he went through the Piccolo's training camp, so he matured and adapted very quickly)
ChiChi probably prevented him from training too when she saw everyone die
As a result of points 3 and 4, he probably got even weaker than he was or maybe maintained the same power level for most of his live
In the postapocaliptic world he also had to worry about getting food for ChiChi, Ox King, and knowing his good heart, for many other people
Even during the Cell saga Gohan had all the "I hate fighting" mindset when he hit puberty, so in the future like that the mindset was probably even heavier and because of that he didn't train as well