Your observation appears to be spot on. $10-20 iems such as the Urbanfun Hifi were en vogue two years ago but the addition of drivers increased production cost and sale prices. We first reached the $50 sweet spot that moved fast to $200 - $300.
As to bass: the music reproduction should be as realistic as possible to me. An overblown bass hurts my perception. Example are the NiceHCK M6: a capable hybrid with an overdone bass.
For the longest time, I had no idea of FR graph interpretation. This changed because of
- My Sennheiser Momentum in-ear, my first >$100. I didn’t like the recessed vocals and found a correlation with the FR graph (V-shape).
- I realized that my $$10-$20 all had such a FR graph.
- The KZ ZS6 with a treble peak that hurt my ears. The graph made this visible (later I learnt that micropore tape helps; graphs indicate the modding results).
The V-shape became a pattern I tried to avoid before I even read up on the information such a graph offers. In the end, the graph characterizes the basic flavour of an iem and may act as an early warning system for the potential buyer.
As a pseudo “audiophile” with shallow pockets I was looking for the budget end-game iem. I was recommended the UE900S ($399 list; $179 massdrop) by an expert. In order to go a step up, you allegedly need to pay 1000-2000 Euros more (many will argue that, I simply don’t know). These are poorly built but sound great. 4 Knowles BAs, no DD. The bass is just fine, very dry. But overall, these and also the highly rated Brainwavz B400 just don’t sound as natural as a good single DD. I’d call this kind of detailed sound “fragile” or “sophisticated”.
What has become very important to me is size/fit. I really like the Brainwavz B200 v1.: very small, very comfy, and the 2 BAs deliver a dry enough sound with a nice low end, which I prefer over the B400’s. With the price increase in the budget segment, the sizes increased, too.
In the end, I tried to do what you did (but at a lower level): get the end-game iem and enjoy it while being able to ignore the ever changing trends.
I am presently weeding out iems and try to give them to a charity (which is not as easy as it sounds). Surprisingly, I am more attached to my old $10-20 iems than the $40-50 fare.
Right now, I am enjoying the cheap Shanling M0 player with the cheap Focal Spark.