I think it'd largely fall down under accessibility. From what we've seen, several of the technologically advanced countries actually have true mages, but instead use the technology/hextech they've created or have had access to. Mages, as we have been told, aren't all that common in regions other than Ionia and the blessed isles. Piltover and Zaun are, so far, the most advanced cities that are still intact. Orianna can't really be considered a mage, as she actually operates entirely based on technology and hextech. Heimerdinger doesn't really use magic, but rather invents and maintains technological weapons/creations... Jayce's isn't magical in nature either. Ezreal is the only mage... and even he is largely unaware of this potential (the gauntlet awoke that potential but he doesn't expand on it beyond the use of the gauntlet)... From that we can assume that, much like a muscle if not exercised, the mages steadily lost aptitude as technology increased due to people not needing to use it anymore, thereby largely forgetting its presence, as well as not thinking they'd have the potential to use it. Therefore the "mage gene" (lol) might've been more prolifically stamped out/suppressed in such countries.
Zaun has Janna, yes... but she's not human, nor is she really even born of Zaun, she's a spirit that seems to have originated around Bilgewater before migrating to Zaun.
In other cultures (ignoring Ionia for now... as well as the Blessed Isles), it's likely that if one is born with magic, to a level that is actually noticeable, they'd be thrust into learning and practicing their magic, rather than learning how to operate machinery. This would likely hold more true for Noxus and the secret faction of Demacia (as these two would seem to be the most likely to have any form of technology i.e. trailing far far behind Piltover and Zaun, but still ahead of the other countries).
The more magically inclined regions (lol, still gonna ignore Ionia and the Blessed Isles) i.e. the Freljord, Bilgewater, and Shurima have a common theme of a harsher, more demanding environment, while also having extremely limited access to technology, seem to generate more mages/magical phenomenon likely due to the "mage gene" not being stamped out, with those who develop an affinity towards magic actively being encouraged to practice it.
Now let's go to Ionia... Ionia is unarguably the most magically prolific continent.. the norm is to possess magic at some level. However, at the same time, they are the most in-tune with their environment and nature... This is due to the culture, which likely ties in how they view magic... as such magic suffuses everything, the people are able to work alongside the lands, thereby seemingly not necessitating much advanced tech of any sort.
The Blessed Isles is largely ruined... therefore we can't draw too many conclusions, but in the past they were also quite in tune with magic, while also being (seemingly) technologically advanced for their time. Therefore, arguably if they hadn't encountered the ruination, they might've been your best bet.
It's not unlikely that there are people who do use a combination of magic and technology in their day to day life, in fact it's highly likely (especially if it's weak magic), however Champions will be a harder example due to them being iconic by themselves. It's likely we will eventually get a champion who combines both tbh.
My thought is that if a person has magic that they can use offensively with actual control, likely won't have much time invested in learning to operate devastating/dramatic technologies (and vice versa)... so likely if/when we come across such a Champ... it will be a relatively simplistic form of technology or relatively weak magic.
As a sidenote... erm.... Targon does exist (the celestial country, not the denizens of the mountain on the mortal plane)...however I'm hesitant to mention them due to their technology being so far advanced and above everyone else, and so highly combined with magic... that it essentially IS extremely high level, powerful magic.
I probably should add that there seemingly ARE more regions than we currently see on the map (as in more continents, if what has been teased in past Riot comments is to be believed), so there is a chance of a magically inclined country with advanced technology.
and 
, but finishes his enemies with energy rays like 
.
all fit this description since yordles are inherently magic. And hextech, which accounts for most of the technology in the game anyways, is directly powered by magical Brackern crystals.
