Uhm, I was talking about Goku vs Luffy, but mmk.
I would factor in Piccolo's Ki Blasts as an advantage vs Gear 4th if they were even remotely close in stats, which they are not. Luffy in Gear 4th has durability nearly doubling Piccolo's AP (Piccolo's AP is roughly 55~58% Luffy's Dura). projectiles can be evaded due to Luffy's speed advantage by entering Gear 4th + pre-cog and the AoEs can be blocked when taking the previous statement into account. Meanwhile, Luffy's attacks, especially in Snake-Man, would be incredibly difficult for Piccolo to evade seeing as how they drastically increase in speed the more they stretch and turn.
And Luffy's flight in Gear 4th works as any pseudo flight and isn't going to hinder him against Piccolo. And in regards to Piccolo's own homing attacks, Luffy could easily use the same tactics Goku did against him. Piccolo isn't an experienced combatant by his time fighting against Goku, in fact, he's an amateur and made many, many mistakes in his fights at that point that led to him taking damage.
Not to mention that his massive AoE attack took an incredible amount of time to prepare (several pages... Tien had time to make a hole and push everyone into it before Piccolo was ready to set it off), and it left him seriously drained.
So where are these so called advantages Piccolo has? As I can see, he has Regenerationn (VERY LIMITED. You can't tell me he can spam that when he's already at his limit after restoring an arm), "better" flight which is minuscule against Gear 4th, and range (which doesn't matter since the maximum starting distance is 4km according to SBA)
Luffy's advantages in Gear 4th include: ~2x Higher AP and Durability (via Gear 4th), Speed boosts via G4, Precognition and the ability to sense his opponent's intentions, Combat experience, Statistics Amp, High resistance to blunt force and some resistance to piercing attacks (effectively making all of Piccolo's physical strikes useless).
So yes, mid-diff. If you want me to argue all of Piccolo's tactical flaws at this point, I'll be happy to.
"spam ki blasts for as long as he wants". Wank, and bs.