There are far too many intangibles to make a call on because they don't apply to both equally. OEB has been there since time immemorial and the sport has changed immeasurably during the time he's been on the World Cup circuit. There are new formats and comparatively speaking more races as a result. There is more travel and more different competition. I think Martin has faced competition that's as strong as Poirée, personally, but the difference is that it isn't the same people all the time to really provide the same head to head competition as it was in the OEB-Poirée days - one week the man in super form is Schempp, one week it's Bø, one week it's Shipulin, one week it's Fak, one week it's Svendsen, whoever. For several years, he's faced strong opposition but never anybody who was consistent enough to threaten him season-long in the total score like Poirée could Ole. The level has also changed as new competition formats have developed - you look at how a men's mass start was raced 10-15 years ago vs. how it's raced now, and there's a world of change as now the mass start resembles somewhat the way the skiathlon worked, with everybody working attrition-wise through the prone bouts to thin the field, very few try to go hard during the prone rounds in case they pay for it later, whereas in time gone by people were winning mass starts even on fairly good days with 3 or 4 misses, which is rare now - also the old adage of getting your misses in early is very appropriate as you can more likely catch back on while the others are skiing within themselves before ratcheting up the pace in the last couple of laps. It's taken a bit longer for the women's mass start to get there but it seems to be going the same way, with people like Dahlmeier using Tora Berger's old energy conservation method leaving a monster final lap in the legs once you've got the field spread out so it's easier to find the space to go all out.
Then you have that OEB also has that whole other string to his bow in the form of his XC successes, which Martin has never replicated, or even really sought to replicate. He's had a few goes at it, sure, but usually in early season races when form isn't really there or even meant to be. Also I got the impression from those that the short bursts and intervals created by the shooting are more key to Martin's races than they were for Ole at his peak, because he would frequently be strong at the 7,5k mark only to fall away significantly in the second half of the race. Kaisa Mäkäräinen always said that the 10k was roughly her threshold in the XC before she'd start to fall away because of the lack of the recovery periods created by the shooting in biathlon, so Martin likely suffers in the same way, but more obviously as Kaisa has posted better XC results than him. Maybe he'd be a better team sprint competitor than 15k free for that reason, I don't know.
The other thing is Ole's longevity. He's one of those people who lives and breathes his sport. His life has revolved around it for two decades now, and with first Santer and now Domracheva both his partners have been on the circuit too. Those statistical records look pretty daunting, because of his longevity, and certainly they looked completely unachievable a few years ago. Fourcade has a balance of life away from the skis, his family are at home and he doesn't come across as being as driven as OEB, however while a few years ago he said he wouldn't chase records, I think the backlash against him for making the sport less interesting in the last couple of seasons has made him a bit more ruthless, as if to assert his domination. After all, what's he supposed to do, start deliberately losing? He's not a quieter Magdalena Neuner type (judging the best female biathlete is much harder for the reason that Forsberg holds all the statistical records, but didn't even become a biathlete until quite late; Neuner was the best in terms of stats like wins-per-starts and retired because she'd won all there was to win without taking statistical records, before even reaching the age Forsberg was when she first picked up the rifle) because he's already won all there is to win - multiple Olympic titles, World Championships and six straight World Cups, some of which at a canter - several times over and is still motivated to go out there and push for more, whereas she was contented with her lot and shied away from the pressure to go for statistical records that are far less daunting than Ole's.
But then at the same time, Ole has been a long way from being the best or fastest biathlete on the circuit for several years now and still found ways to win and podium races, competing in a completely different way to how he did at his peak, adapting and changing tactics to go with the times and reflect his own changing skillset as he grows older. Fourcade hasn't had to do that yet, so it remains to be seen whether he has that adaptability.
Idunno, it's like comparing Prost's 4 F1 titles to Hamilton's or Vettel's. Statistically speaking, Prost had fewer rivals at the title-winning level (Senna, Piquet, Mansell for the most part, early on Rosberg and Lauda but at that point Mansell had yet to emerge) than the current crop (the grid at one point in the early 2010s had Schumacher, Button, Räikkönen, Vettel, Hamilton, Alonso, Rosberg jr), but the other title winners of Prost's time will likely be far more revered in posterity. Variables were different, and in fact Prost was one of the innovators of more tactical racing that led to the style that developed over the 90s and 00s of pit-stop racing. Or saying, who was France's better Tour champion, Anquetil or Hinault? The sport is the same in design but not quite the same in character now. Ole is definitely the biggest legend of the sport, but that isn't the same as necessarily being the best.