Diddys jab sucks. And frame 3 is just good enough to not be slow.
Also did you ever look at the frame data of other characters?
Let's look at Fox for example.
Jab 2 (-1)
Dashattack 4 (-5)
Ftilt 6 (-4)
Dtilt 7 (+3)
Utilt 3 (-3)
Fsmash 13 (+1)
Usmash 8 (+3)
Dsmash 6
Nair 4 (-4)
Fair 7 (+1)
Bair 9 (+4)
Dair 5 (-12)
Uair 9 (+6)
Grab 6
DashGrab 10 (+2)
Overall Fox has a +9 frame advantage on Diddy for these moves.
Then there's Mario, Luigi, Doc, Marth, MK, Mii Fighter, Pikachu, Sheik, and others who have really good framedata too.
Move | Mario | Luigi | Sheik | Fox
Jab | 2 | 2 | 2 | 2
DashAtk | 6 | 4 | 5 | 4
Ftilt | 5 | 5 | 5 | 6
Utilt | 5 | 5 | 5 |3
Dtilt | 5 | 5 | 5|7
Fsmash | 15 | 12 | 12|13
Usmash | 9 | 9 | 11|8
Dsmash | 5 | 6 | 11|6
Nair | 3 | 3 | 3|4
Fair | 16 | 7 | 5|7
Bair | 6 | 6 | 4|9
Uair | 4 | 5 | 4|9
Dair | 5 | 10 | 15|5
Grab | 6 | 6 | 6|6
DashGrab | 8 | 8 | 8|8
Advantage on Diddy |
8
|
15
|
7
|
9 Overall frameadvantage against Diddy, Pikachu has a
-2 disadv, and Marth a
-8 disadv. (just to compare more numbers)
Now look at Diddy Kong... he's a quick and nimble monkey. It makes sense that his framedata is good and fast. It would be stupid otherwise. His character can't be slow, it wouldn't make any sense. That's one thing he has going for him which makes him fundamentally a character who's great in the game. Though in Brawl he lacked a little range and there were less crazy combos, so he had to rely on bananas for most MUs to do well. And also frame 6 standing grab and frame 8 dashgrab is the norm for most characters, so again it wouldn't make sense to make Diddy slower.
A better thing would just be to nerf his uair a little knockbackwise, and maybe think about his fair and sideB, because fair is really safe and shuts down so many appraoch attempts, and sideB's grabrange is still great... it goes way below his animation, catching ducking/small opponents easily, and the grab holds on for a long while, so he can grab you even at almost the end of his sideB, where you might not expect it, so rolling away from that often still gets you grabbed (or kicked).
Diddys (not sideB) grabrange is actually really bad. I think if he gets nerfed a few frames on fair/sideB grablength and get's different knockback on uair it would be good enough to fix everything people have against him perfectly (okay, some might still hate stuff about Diddy but ah well, (almost?) every character has haters). Oh and I guess they could give his uthrow a little more knockback or endinglag so he can't follow up as easily. Maybe 1-3 more frames on dthrow as well to make it a little more difficult.
...But now this goes way too deep into this.
The point was Diddy has great framedata, yeah, but he's not alone, and he should be fast, just looking at him / his character. The framedata is not necessarily the problem here, he'd just need a few little other fixes to make people hate him less.