Well.... your ears will seperate direct from reflected sound, but the standard continuous signal measurement of frequency response won't.
So what your ears "want" to hear is a relatively flat frequency response.
If you take a speaker that measures "flat" in an anechoic measurement (ie with no reflected sound- just the speaker alone) - and you place it in a typical listening room / living space, your f/r measurement will then be altered by the various reflections reaching the microphone from all around... so what you are measuring is the direct sound + the reflected sound.
Any reflected sound that is sufficiently delayed, will be "discounted" by our brains as part of the primary signal - and we then interpret it as ambiance/soundstage... but it does not factor into imaging/detail.
However the standard F/R method does not take this into account.
In your typical domestic space - much of the higher frequency reflections will be reduced by furnishings, curtains, etc... whereas the bass will typically bounce around more freely (unless the room is specially - and expensively - treated)....
So you will be adding more bass to the flat base signal, than highs - and the end result for a "good" (anechoically flat) speaker, in a real room, will tend towards the tilted bass high treble low profile.
If you have a flat F/R in room, then typically the base direct signal from the speaker is not flat but tilted towards the highs - hence some will characterise it as "harsh".
However there is always the matter of adjusting for taste! - it used to be quite common to see people using the analogue equalisers back in the day, to tune for a "smile" response with boosted bass and highs, and lower midrange - not my cuppa tea, but each to their own...
Key thing in optimising speaker to room setup, is to try to ensure that reflections are sufficiently delayed so that they don't impact on the direct sound and therefore imaging / detail.
That is why many like to place their speakers further from back and side walls... that delays the reflections! - however if the speaker is well damped, and has negligible output to the sides and rear, then this may be a non issue (or in the real world, a lesser issue).
Also it is nice to have an ample "soundstage" - ie: reflections are not a total negative - quite the contrary... reflections (when properly delayed as discussed earlier) provide the fabulous soundstage that really good setups have.
So we then have various speaker designs that vary in terms of directivity - ranging from fully "omnidirectional" (ie speakers with equal output in all directions- including back!) - which require careful placement and/or treatment to get the reflection timing right. (further from the wall, or absorbant / dispersing treatments used)
To highly directional designs... where if you aren't right "in line" with the speaker, you get a substantially lower output.
The worst of the output from speakers is uncontrolled resonances from the cabinet... well designed and damped speakers substantially minimise that...
My personal preference is wide dispersion speakers, and to place them with caution in the room - thereby getting the expansive soundstage from the reflections while still getting the imaging and detail.
End result "In Room" is still the slightly tilted F/R...
So yes, if your measurements are showing a flat F/R "in room" - it is cause for suspicion - either the speaker is anechoically "non flat" - or the room is highly reflective - typically neither of those is optimal.... (but, there is no accounting for tastes... some people like it like that)
