The major difference between DPS and Burst is almost non-existent at this point.
You have your standard burst mages/assassins, but since damage is THROUGH the roof items like
on ADCs just makes them even more bursty on top of double crit yasuo with
. It is almost like a race who can kill faster at this point. There is no real DPS/Sustained damage by anyone is league anymore. It is just spammy burst and fast killing. That is why when a fighter/bruiser builds
They are literally unkillable because they get just enough tankiness to survive burst and do it themselves later.
Assassins and burst mages are supposed to destroy the back line. Not marksmen. Marksmen are the sustained DPS to break frontliners and keep sustained damage for the team if the burst is dead. Honestly, the entire itemization of league of legends needs to be reworked to remove burst on champions that DON'T need burst at all.
what do you mean i should not kill a team in 3seconds 30mins into the game? i mean its deep late game 30mins into the game right? KAppA.
What do you mean my Kha'zix died as soon as he touched the ground to kill the enemy adc?
What do you mean the enemy adc gets a 700hp shield INSTANTLY because support items are a tad bit stupid atm? i mean every champ in the game can do 2.3 k dmg instantly to kill an adc through its shields before the adc kill the other champ in 2seconds with 4 750dmg crits
Not quite all of them.
or 
to name a few.
What is this burst DPS you're talking about? I'd like to get in on that deal.
etc. Champs that are only DPS are much less useful due to them needing to stick onto a champion to be able to deal the majority of their damage, which is why top laners are sent to split push because of how hard it is for them to reliably stick in a fight to do their damage when most team comps can simply peel them off.
do incredibly high damage in seconds. They burst down champions which is probably not the marksmen class is intended for.