So I looked at the numbers for Lacazette, Costa, Suarez, Aguero and RvP.
Costa has only been at Chelsea for 3 seasons, Suarez at Liverpool for 3.5 seasons and I took RvP's last 5 seasons in England. Lacazetta I did analysis for his last 4 and 5 seasons, his numbers changing slightly because his season when he was 21 had less minutes and appearances so I've done both.
205 games, 139 goals with 39 assists (178 direct involvement) in 15,230 minutes.
15,230 / 178 = 86 minutes per goal
133 games, 82 goals with 53 assists (135) in 11,324 minutes.
11,324 / 135 = 83 minutes per goal
188 games, 119 goals with 42 assists (161) in 14,557 minutes.
14,557 / 161 = 90 minutes per goal
120 games, 58 goals with 24 assists (82) in 9,794 minutes.
9,794 / 82 = 119 minutes per goal
Last 4 seasons:
183 games, 113 goals and 35 assists (148) in 15,097 minutes.
15,097 / 148 = 102 minutes per goal
Last 5 seasons:
220 games, 117 goals with 45 assists (162) in 17,857 minutes.
17,857 / 162 = 110 minutes per goal
Obviously pinch of salt with Lacazette as he's only played in Ligue 1 and regardless of what people say I do believe that the Premier League is harder and a higher level than Ligue 1.
In any case, I feel like Giroud's 107 minutes per goal is really good but that Van Persie, Suarez and Aguero are clearly on another level above Giroud's. Still, I don't think Giroud's 107 is bad at all in any way shape or form and I'm sure if you measured him against other strikers in the PL apart from arguably the Top 3 of the last 10 years he wouldn't fall short.
Don't forget that we've won 3 FA Cup finals with him at the top, getting assists and a goal in each final. So he's not been all bad and he actually comes ahead of Costa.