The advanced stats don't necessarily bear that out. Looking at their Wowy from when RoR joined the Blue to now, they both have higher advanced stats together than separate. They have actually played together at about half of Tarasenko's 5v5 TOI over this period.
TOI With : 779
TOI Without: 731
CF% With: 52,96
Tarasenko w/o-49.93
ROR w/o - 51.55
GF% With: 60.87
Tarasenko w/o-39.98
ROR w/o - 62.5
xGF% With: 54.18
Tarasenko w/o-51.5
ROR w/o - 49.56
*Credit to natural stat trick for all stats
Now this isn't a perfect analysis as its possible they played less time together when Tarasenko was playing injured and not as well, which would skew the results. But overall, they mostly have a positive impact on each other's advanced stats, with O'Reilly fairing much closer when alone to how they are together. In fact, O'Reailly has a slightly better GF% w/o Tarasenko.
None of this is to say they should or shouldn't be played together. Given how equally well ROR does w/o Vladdy, it makes sense to use Vladdy to bolster another line. But they aren't a terrible together, at least from an advanced stats viewpoint. If that makes sense to make the other lines work, we shouldn't be precluded from trying it based on past performance.