tl;dr - Jakobi is explosive enough (37" Vert Jump / 1.56s 10yd split). He just has terrible top end speed.
I got so confused a few months ago after finding out that Jakobi had the 3rd highest avg speed out of 89 WRs (with
min 200 routes) after 1 second post snap (through Week 13 this season - Bourne was 1st). It didn't make too much sense because he just seems so slow (unless they count motion plays like jet sweeps - hope not). It wasn't until I started analyzing the historic* 10yd splits of the recent combine that it all made sense. Despite his slow 40 time, his 10yd split is pretty fast. His 1.56s split is faster than a lot of these Pro Bowlers.
mike evans 1.6
kupp 1.62
davante adams 1.64
justin jefferson 1.57
deebo samuel 1.6
SDiggs 1.53
(pro day so prob hand time and inaccurate / not electronic)
Ja'maar 1.59
Tyreek 1.5
As far as the 10yd split is concerned, he's officially the 2nd fastest on the Patriots, with JJones at 1.47 (which
until this year* is REAALLLY fast) the only one faster. CDavis (1.51), SWade (1.53), KWilkerson (1.45!!!) were all pro days, so probably hand times, which are going to be inaccurate, so I'm not going to count them. Here are other Patriots of note:
Bourne 1.61
Agholor 1.59
Edelman 1.52
Gronk 1.58
Mccourty 1.6
The guy has good acceleration from a stop (until a governor kicks in early) and is kindof explosive, but just has terrible top end speed (heck if there's such a thing called medium end speed, it wouldn't be great, either). It's probably why his YAC is faaarrr from great (that and his elusiveness / ability to break tackles is subpar). It's clear to me now that he needs to work with a track coach to improve his cadence (steps per minute). Peaking at high 250s ain't gonna get it done at his height - he's running like a 400m runner.
Side note - imho, I have a feeling Wilkerson has a lot of untapped potential (1.45ht 10yd, 39.5 VJ, 6.68 3cone) and could conceivably be the next good slot receiver assuming he can improve the drops. He just needs more opportunities and time and a move away from his reps at mostly X. Barring an injury, it's probably not going to happen this year (or ever) since Bourne needs to be in there more.