How's it going to lure anything if it's just running an extremely standard 4 attack set that most people are now aware of? If anything a NP set is a lure, as it lures Chansey. Plus, either the NP set and the 4 attack set can clean up late game without the need to set up - one less coverage move is rarely going to swing it.You're looking at it the wrong way. Raichu's primary function is to support its teammates. In the early game, it's supposed to lure out and weaken Pokemon like Ferrothorn and Ground types so that Koko and Rain sweepers have an easier time cleaning up. In the lategame, if Raichu is still alive, it's pretty much going to pick off weakened Pokemon. It's not going to have the time to set up Nasty Plot.
Tbolt 2HKOing Tar is quite frankly, unacceptable and nowhere near as important as OHKOing it. Tyranitar cancels Rain so OHKOing (or heavily damaging it) is extremely, extremely, extremely crucial.
As I keep mentioning, there is a whole team, you can switch something into TTar as it switches in itself. Electric Terrain isn't everything when it comes to Raichu - Raichu has decent speed already and E-Terrain is short lived, so it's not like with a cautious switch you're always wasting a massive opportunity. Also, if you do set a Nasty Plot, then this happens:
+2 252+ SpA Life Orb Raichu-Alola Surf vs. 0 HP / 0 SpD Tyranitar: 302-356 (88.5 - 104.3%) -- guaranteed OHKO after Stealth Rock
You're clearly unconvinced on a Nasty Plot set having any real viability or having any opportunities to set up, which having played it I know it can (it's so easy to force pokemon out due to the speed and STAB boost under E-Terrain), so I won't drag this out any further. However, I've provided legitimate and valid counter points at each turn so people should be able to see it's not as cut and dry as just the one set working. To me, both sets are viable - as I keep saying they have different functions, so it all depends on what better serves someone's team. Paired to a rain team for example, there's plenty of other fast swift swimmers who can run four attacks already - have Raichu with set up (or vice versa) to wall break really isn't a half bad idea.