In an absolute garbage-tier league.
Looking at that list of his games:
1. Zlatan had 4G + 2A in 8 games against the best non-French teams he played in Chelsea, Shakhtar, Real Madrid and Man City.
2. Against the 4 other French teams who seem to have had solid seasons (Lyon were a solid +24, Nice were +17 and while Lille were 4th in GD, they only conceded 27 goals, which implies solidity defensively, Monaco were only +7 but finished 3rd and came off a fine season), Zlatan posted 7G + 2A in 8 games.
So, if we assume the foreign teams in point 1 are roughly equivalent to the average of the top 8 in England (City are there, Madrid fair bit better, Chelsea (though in the CL not as awful) last year fair bit worse, Shaktar probably around the level of 5th-6th) and that the 4 domestic sides I included are roughly equivalent to average bottom half sides (with Ligue 1 having such a down year), you'd basically have a decent 14 games cross-section resembling the Prem. Probably a shade tougher but he had Verratti and Di Maria there to create so it's not unfair to be a bit ungenerous.
Zlatan's "Top Level Season" numbers would be 11G + 4A in 16 games. Double the numbers since 32 games would be about a normal healthy season for a striker with a couple of EL and Cup rest, a suspension and then 2-3 games injured and we have a season of
22G + 8A.
Not proper dominant, but basically just below the goalscoring feats of Kane (25) and Vardy (24) and Aguero's 22 in far less game time, but with more assists than Vardy (6) and far more than Kane (1) or Aguero (2). Or looking at other target 9s, Giroud had 16G + 6A and Lukaku had 18G + 6A.
That seems totally plausible to me, that at 34 Zlatan would be Giroud with 30% more goals or 90% of a Kane/Vardy goalscoring but far more creative and likely to provide an assist. On the whole, we'd be talking about a striker at but not above the level of the top 5 of Kane, Aguero and whoever jumps up next year, likely 2 from a healthy Sturridge, bouncing back Diego Costa or an improving (as a young player or with better teammates) Lukaku.
Having only seen about 5 PSG games last year, mostly CL, I'd say this sounds right. Zlatan's skills are incredible but he has definitely slowed down and PSG played a fairly languid, conservative style in which possession was largely used to defend until a truly killer ball was available or a fullback/winger could get in behind. If you watch the video of Zlatan's goals, he scored a lot of tap ins, which PSG created due to the brilliance of Di Maria (and Verrati) and physicality/penetration of Matuidi, Cavani and at times, Lucas and Aurier.
TLDR: In a normal 30-35 Prem game season, assuming a slight decline from age 34 to 35, coming off a Euros, I would put Zlatan's expected numbers for us at 20G and 6A, which would make him likely the 2nd-4th most productive striker in the league.