[OnePlus 3 Themes, Apps, and Mods] chdloc:
Not that it will give you much comfort, but the (stock) camcorder audio of the Nexus 5 was much worse as it not only suffered from aggressive noise suppression, but it could not handle loud environments, either. It is not 100% obvious from your recording, but the main culprit seems to be the noise suppression. I do not have an OP3 to test but to try to turn off noise suppression I would add the following line to /system/etc/audio_platform_info.xml inside the <acdb_ids> and </acdb_ids> tags:

<device name="SND_DEVICE_IN_SPEAKER_STEREO_DMIC" acdb_id="35"/>

and play around with the acdb_id value. 35 appears to be the default. The other values that the OP3 seems to have defined can be found in the audio HAL's sources (hardware/qcom/audio/hal/msm8974/platform.c):

[SND_DEVICE_IN_HANDSET_MIC] = 4,
[SND_DEVICE_IN_HANDSET_MIC_EXTERNAL] = 4,
[SND_DEVICE_IN_HANDSET_MIC_AEC] = 106,
[SND_DEVICE_IN_HANDSET_MIC_NS] = 107,
[SND_DEVICE_IN_HANDSET_MIC_AEC_NS] = 108,
[SND_DEVICE_IN_HANDSET_DMIC] = 41,
[SND_DEVICE_IN_HANDSET_DMIC_AEC] = 109,
[SND_DEVICE_IN_HANDSET_DMIC_NS] = 110,
#ifndef VENDOR_EDIT
[SND_DEVICE_IN_HANDSET_DMIC_AEC_NS] = 111,
#else
[SND_DEVICE_IN_HANDSET_DMIC_AEC_NS] = 41,
#endif
[SND_DEVICE_IN_SPEAKER_MIC] = 11,
[SND_DEVICE_IN_SPEAKER_MIC_AEC] = 112,
[SND_DEVICE_IN_SPEAKER_MIC_NS] = 113,
[SND_DEVICE_IN_SPEAKER_MIC_AEC_NS] = 114,
[SND_DEVICE_IN_SPEAKER_DMIC] = 43,
[SND_DEVICE_IN_SPEAKER_DMIC_AEC] = 115,
[SND_DEVICE_IN_SPEAKER_DMIC_NS] = 116,
#ifndef VENDOR_EDIT
[SND_DEVICE_IN_SPEAKER_DMIC_AEC_NS] = 117,
#else
[SND_DEVICE_IN_SPEAKER_DMIC_AEC_NS] = 43,
#endif
[SND_DEVICE_IN_HEADSET_MIC] = 8,
#ifdef VENDOR_EDIT
[SND_DEVICE_IN_HEADSET_MIC_FLUENCE] = 16,
#else
[SND_DEVICE_IN_HEADSET_MIC_FLUENCE] = 47,
#endif
[SND_DEVICE_IN_VOICE_SPEAKER_MIC] = 11,
#ifdef VENDOR_EDIT
[SND_DEVICE_IN_VOICE_HEADSET_MIC] = 16,
#else
[SND_DEVICE_IN_VOICE_HEADSET_MIC] = 8,
#endif
[SND_DEVICE_IN_HDMI_MIC] = 4,
[SND_DEVICE_IN_BT_SCO_MIC] = 21,
[SND_DEVICE_IN_BT_SCO_MIC_NREC] = 122,
[SND_DEVICE_IN_BT_SCO_MIC_WB] = 38,
[SND_DEVICE_IN_BT_SCO_MIC_WB_NREC] = 123,
[SND_DEVICE_IN_CAMCORDER_MIC] = 4,
[SND_DEVICE_IN_VOICE_DMIC] = 41,
[SND_DEVICE_IN_VOICE_SPEAKER_DMIC] = 43,
#ifdef VENDOR_EDIT
[SND_DEVICE_IN_VOIP_MIC] = 43,
#endif
[SND_DEVICE_IN_VOICE_SPEAKER_QMIC] = 19,
[SND_DEVICE_IN_VOICE_TTY_FULL_HEADSET_MIC] = 16,
[SND_DEVICE_IN_VOICE_TTY_VCO_HANDSET_MIC] = 36,
[SND_DEVICE_IN_VOICE_TTY_HCO_HEADSET_MIC] = 16,
[SND_DEVICE_IN_VOICE_RX] = 44,

[SND_DEVICE_IN_VOICE_REC_MIC] = 4,
[SND_DEVICE_IN_VOICE_REC_MIC_NS] = 107,
[SND_DEVICE_IN_VOICE_REC_DMIC_STEREO] = 34,
[SND_DEVICE_IN_VOICE_REC_DMIC_FLUENCE] = 41,
[SND_DEVICE_IN_USB_HEADSET_MIC] = 44,
[SND_DEVICE_IN_CAPTURE_FM] = 0,
[SND_DEVICE_IN_AANC_HANDSET_MIC] = 104,
[SND_DEVICE_IN_QUAD_MIC] = 46,
[SND_DEVICE_IN_HANDSET_STEREO_DMIC] = 34,
[SND_DEVICE_IN_SPEAKER_STEREO_DMIC] = 35,
[SND_DEVICE_IN_CAPTURE_VI_FEEDBACK] = 102,
[SND_DEVICE_IN_VOICE_SPEAKER_DMIC_BROADSIDE] = 12,
[SND_DEVICE_IN_SPEAKER_DMIC_BROADSIDE] = 12,
[SND_DEVICE_IN_SPEAKER_DMIC_AEC_BROADSIDE] = 119,
[SND_DEVICE_IN_SPEAKER_DMIC_NS_BROADSIDE] = 121,
[SND_DEVICE_IN_SPEAKER_DMIC_AEC_NS_BROADSIDE] = 120,
[SND_DEVICE_IN_HANDSET_QMIC] = 125,
[SND_DEVICE_IN_SPEAKER_QMIC_AEC] = 126,
[SND_DEVICE_IN_SPEAKER_QMIC_NS] = 127,
[SND_DEVICE_IN_SPEAKER_QMIC_AEC_NS] = 129,
[SND_DEVICE_IN_THREE_MIC] = 46

I would start with "4" and, at least initially, avoid the ones that are tagged with "NS", "AES", or "FLUENCE" in the above list. You will need to reboot your phone after each change, but make sure that you don't change the default file permissions (rw-r--r-- or 644).