They are very odd choices and tell you a bit about the poster. Specifically in both cases they're kind "off-brand". The big MOBA with significant multimedia success (rather than merely aspirations) is League of Legends. Not only is it bigger than DotA 2 (and likely DotA) ever has been, it's actually been successful with things like Arcane (whereas the DOTA anime, also Netflix, is not particularly popular or noteworthy). Further, the massive fanbase of LoL crosses over more with tabletop RPG players, I would suggest, and it shares far more of its central aesthetic with MtG and modern D&D than DotA 2 does.
The Witcher as a TV series is popular but obviously not Game of Thrones or LotR popular. As a videogame it's also popular, but not The Elder Scrolls or League of Legends popular, let alone World of Warcraft popular (over the last 15 years). As books they're even less popular in the West (if much discussed).
Anyway yes even if looking at specific games/TV shows/etc. there's a pretty long list to go through in terms of being influential on modern D&D before you'd get to either DotA or the Witcher. Also I think it's worth noting that even just focusing on games, TV shows, etc. is outdated - I suspect Critical Role and its audience will be more influential on future D&D aesthetic and design decisions than most games/TV.
It's not just an issue in fantasy writing, either (though it certainly is happening there to a degree), but also in fantasy art. There's been a sort of drift towards almost a "shared aesthetic" among a lot of fantasy art over the last few years, one which is sort of exemplified by Arcane (the Netflix show based on League of Legends) and can also, I would argue, be seen in Critical Role products and increasingly in D&D (indeed the 5E PHB was already heading that way) and MtG. I think MtG was in many ways responsible for starting this trend. There's still tons of art that doesn't really fit it, or is only a branch of the family tree, but we're talking about sort of slightly exaggerated aesthetic with its roots as much in comic books and graphic design than fine art (even if fine art techniques are used to create it), with a lot of bright colours and warm metals, inevitable steampunk/magitech devices, clothing trending towards the stylish and quasi-modern rather than the realistic or historical, and generally a trend away from quasi-realism, but also away from the more extreme stylization of earlier decades. It's kind of becoming an overly safe and standard aesthetic if you ask me, and needs shaking up (and not merely by attempting to revert to some earlier approach).