I think am not 100% what exactly you mean with this post? What would have „showcased“ this IEM vs others to you? What do you mean by „ideal“ frequency response?
You mean you found the signature was not your taste? Or „boring“ in general? BCan you please specify a bit? I am just wondering because from the graph the L9 signature does not seem to be this „neutral“ or „boring“ type. More like a signature that polarizes because of the elevated bass...?
Showcase : Every IEM has a firm "tuning" and they try to convey a capability towards a certain frequency, type of music ,etc. This one did not try to do anything, it was very vanilla.
Ideal Frequency: You have a lot of reviewers that state that frequency curves are the ultimate tool to determine an IEM good vs bad. This IEM had a frequency curve that was deemed by reviewers as the right one. Maybe it sketches out well, but when reproducing sound of a certain type into your ear (each one different and age influences) the result is just again vanilla
Boring: Nothing within the IEM was bad is just did not bring anything that differentiate it, nothing that made say let me pick it up to go listening to....... . Again by looking at the graph you will think you getting something but not really!!
The type of music ( genre), production period (60's,70's, 80's, remastered or not), cable, iem, tips, ear structure, age influences the reality of an IEM signature and as such my take is based on that