Not really sure how to reply to this if you think the Sonic is in any way better than the 5. It's got 47 cu ft of cargo space with it's rear seat folded down. 3 more cubic feet than the 5 has with ONLY the 3rd row down. With the 2nd row folded, the 5 has 97+ cubic feet of cargo room. Not really in the same class there. The 5 was redesigned in 2010 and refreshed in 2012, so it's not a 10 year old design BTW, but I agree with you that it's not comparable with the newest stuff when it comes to ICE (in car entertainment), but that is actually one of the reasons I chose it oddly enough. Every car I've driven with a touch screen for everything has been pretty annoying. Until Apple Car Play or the Android system (maybe) is in every car, I want nothing to do with more modern car interfaces, because they are all atrocious and unresponsive. I like the 5's simple system that keeps my eyes on the road instead of buried 4 menus deep on a 7" color LCD looking for something while I drive into a tree hahaha.. The 5 does everything I need it to, no need to reinvent the wheel here, unless you're going to make a better wheel. As far as I can tell, the only one who may have done that yet is Apple.
Back to the Sonic, I'm sure it's great, but the Sonic is based on a Daewoo Korean economy car and has a prehistoric torsion beam rear suspension. It doesn't sound like a bad car, but it's based on older technology than the 5 and it doesn't represent any kind of new innovation over the 5. At all. There is literally not a single thing about it that is "more modern" than the 5, except maybe the more adventurous styling. I have a feeling once the "newness" of it wears off you'd realize the 5 is the better, more sophisitcated car. I use different cars from time to time, so I understand where you're at. Something different often seems fresh and new and "better" even if it really isn't. You haven't had a chance to see all it's warts yet. There's nothing extraordinary about the Sonic at all, trust me. It does get better MPG though (not hard when you're 800 lbs lighter haha). If you enjoy it, that's all that matters, but it's not a good example of something more modern or advanced than the 5, because it just isn't. There are other cars that are, but it's not one of them.
The only cars I'm aware of that are in the same class as the 5 and offer more modern solutions without compromising interior room or handling, are MPV's not sold in the U.S. Here everything else that is newer or "better" than the 5 is either an SUV with less room or much worse handling (or both) or a giant aircraft carrier of a minivan that costs $12k more, weighs 1000 lbs more and drives like a barge. That's why when I bought a car recently after 6 months of research, I still chose a 5. There are perhaps better cars of similar design that don't compromise, but none of them are for sale in the U.S. sadly, so I took the best one I could get.