Believe me or not, I'm a 100% free player on PPS.
As you say, there is no benefit to spend cash on PPS just for 2 tickets.
The R Slayer Card is from an event ticket (login bonus) with card reveal.
I also got a 2nd event ticket from 500k EP (got a R dupe...).
I got 2 N Slayer Cards from the normal gacha.
I did used a trick:
I created new accounts to keep sending low level boss to my main account.
This way I have the 3x MVP bonus and a LOT of reward to level up (coins, normal tickets and wild cards).
210,739 SED x 2.13 Slayer Card bonus x 3 / 100 = 13,466 EP every half hour
about 270k EP every 10h!
It was a kind of "can you do it?" crazy challenge.