I keep getting 1 shot pretty much because of expose. Some little alien dude is running around stunning everyone and 1 shotting them. I rarely get exposes whats going on here? Is it based on equipment?

Some abilities are Exposes that weaken you to another kind of attack called 'Exploit'. They are based on the ability you are using. If you look at your ground abilities, some will say 'expose' and others will say 'exploit' I often had my bridge officers have a few Expose abilities while me and my first officer carried phaser sniper rifles, which would do hideous damage as the sniper shot was also an exploit attack

is it science officer that offers the most exposes normally?

Expose/Exploit is definitely to high.
Two science chars for example.
One uses Heal the other a hold skill
So first Hold to expose, then a sniper shot for exploit - up to 900dmg in tier one
That´s a one shot kill
So where exactly is the other one supposed to fire back or heal?
Even the dmg scale of Flanking and Exploit are to high.
160dmg front
up to 600 dmg Flanking (thats more then 3 times the dmg!!!)
up to 900 dmg with Expose/Exploit (witch takes about 3 Seconds ^^ and does more then 5 times the dmg a normal shot would do)

I can only hope Cryptic will do something about it. Cause all that keeps G-PvP going is teamplay, so that the exploits can´t be used properly. But the higher the Tier, the worse it will get.

Fairly certain your flank damage is wrong. The best I have gotten out of Flanking is a 50% damage bonus with my weaponry.

Exploit damage is massive though, and it should be as there is only a chance that an expose will happen anyways.

A snipe shot from behind with 450-550 dmg is not rare.
To the chance -
Tried it 6 times in a row
5 times it was 1hit kill
1 time i had to freeze him again, then killed him...
Since there is no resi or anything building up, he hit my shields with some dmg ... had about 75% shield energy left...
froze him, then he met his fate
So the numbers do play out.
However, in 1on1 PvP there should be NO ABSOLUTELY NO 1hit Kill. (Only exeption is, that the move is hard, meaning it takes timeor you expose yourself with it etc... something to balnce it out.)
A series of crits, or fast dmg pounding should not kill under 4 sec.
Since the idea is FOCUS fire in PvP. Meaning that Classes like turret engies, healer or other supporter still got something to do. So in 1 on 1 - no 1shot kills.

Sadly further tests have to be conducted by someone else...
I´m lying 8 feet deep in Tier 2