Whether or not it can be called a sneak attack depends on seeing it
Luffy is a frontrunner. No matter how good he looks at the end of this chapter, he's literally in for hell next week
Extreme copium.
This is base Luffy still btw.
Next chapter will only get better because he will inevitably use G5, and we all know how badly G5 clowns TF outta agendas. Oda will hype G5 and very likely also make Imu hype G5. That will happen for at least a minimum for 1 (next chapter), most likely more since Luffy just ate and Loki's still there. So nah. Next chapter will only get better (or worse for you).
Next up, if Imu then starts unleashing new attacks/abilities etc etc after Luffy is in the fight (especially if base), then that automatically confirms that Imu was handling Loki with kiddy gloves all this time. Luffy made him get serious, therefore base Luffy (if he stays in base for some part of the fight) did more in his few attacks some or all of which were base, in 1 chapter, then Loki + Ragnir did in 3-4? Chapters of fighting.
Therefore, possibly base Luffy (dependent on how fast he goes into G5, but G5 is fine too because the powerup is yet to come, that's when the clowning really begins)> Base Loki + Ragnir. Sounds like a W for Luffy still.
Which brings me on to Loki. If a loss is to occur, then his going to 100% hypetool Loki first, like with Kaido's first flame breath on the crew, which at the time was done to add stakes at the crew being cooked, leading to Luffy losing it, then going all out and fumbling it, and losing.
That'll be 2 chapters minimum. So overall, Luffy will be good for I'd say at minimum 3-5 chapters of fighting.
Nope. It simply cannot be a sneak attack. If Imu and Loki were unaware, then base Luffy speedblitz + perception blitz Imu. W for Luffy.