No
_Absolutely not _
The problem here is you are comparing her to all champions and not all marksmen in a vacuum. She is a marksmen support and her abilities are currently in line with other marksmen as they should be.
The thing is most marksmen have their "Utility" ability on their E.
Now I am using utility as a bit of a broad term her, but in general we see it range from mobility (such as
) to CC
) to more unique things

Marksmen with utility (movement, CC other...) on E


Of the 25 champions riot designates as a "Marksmen" I have identified 21 as having followed this trend.
Please note: I didn't really like including the last 3 and think of it more as 18/22 but TECHNICALLY they are marksmen and they do follow the trend
Also note, I am aware there is some overlap such as 
where his E is a long range ability as well as CC, and by this trend his W would fit better.
Now lets look at those who don't fit this "E = Utility" trend.
Damage ability with specific interactions with her core mechanic (spear stacking)
On hit effect, core to his kit
Damaging ability
Damage ability with specific interactions with her core mechanic (poison detonation)
Now what do we notice in common with these 4?
3/4
Are from the original roster. And the fourth,
has the E function almost identically to
. Build up stacks, E to detonate
So really these are mainly outliers due to age, as the the past several years, the trend Riot has adhered to has been very consistent.
We can also note, the two I identified of technically being in the "utility e "
Furthermore, although not as prevalent we have a long established precedent of long range marksmen abilities on W
Marksmen with range damaging ability on W

I would also like to bring further emphasis to
Who are probably the marksmen with abilities that are closest to Senna's (a very long range ability, that applies some kind of effect)
Another trend I noticed doing this, is often ADC steroids are on W which sometimes overrules other trends.
(kind of)
(arguably)
are some quick examples of that