I have been doing some more comparisons between the the handbuilt kernel and the one that comes in the prebuilt.
The prebuilt one shows several modules in lsmod,
Module Size Used by
ftm5 364544 0
heatmap 28672 2 ftm5
videobuf2_vmalloc 28672 1 heatmap
videobuf2_memops 24576 1 videobuf2_vmalloc
lkdtm 61440 0
adsp_loader_dlkm 24576 0
stub_dlkm 24576 1
usf_dlkm 86016 0
native_dlkm 233472 0
machine_dlkm 229376 0
platform_dlkm 2588672 59 native_dlkm
wcd_cpe_dlkm 151552 0
wsa881x_dlkm 73728 1 machine_dlkm
wcd934x_dlkm 503808 1 machine_dlkm
wcd9360_dlkm 348160 0
mbhc_dlkm 102400 1 wcd934x_dlkm
wcd9xxx_dlkm 110592 2 wcd934x_dlkm,wcd9360_dlkm
swr_ctrl_dlkm 49152 2 wcd934x_dlkm,wcd9360_dlkm
cs35l36_dlkm 311296 2
q6_dlkm 1318912 10 usf_dlkm,native_dlkm,machine_dlkm,platform_dlkm,wcd_cpe_dlkm,wcd9xxx_dlkm,swr_ctrl_dlkm,cs35l36_dlkm
swr_dlkm 45056 2 wsa881x_dlkm,swr_ctrl_dlkm
apr_dlkm 253952 5 adsp_loader_dlkm,usf_dlkm,platform_dlkm,wcd934x_dlkm,q6_dlkm
q6_notifier_dlkm 24576 3 machine_dlkm,q6_dlkm,apr_dlkm
q6_pdr_dlkm 24576 1 q6_notifier_dlkm
wglink_dlkm 32768 0
wcd_spi_dlkm 40960 0
wcd_core_dlkm 188416 6 machine_dlkm,wcd_cpe_dlkm,wsa881x_dlkm,wcd934x_dlkm,wcd9360_dlkm,wcd9xxx_dlkm
pinctrl_wcd_dlkm 24576 0
msm_11ad_proxy 45056 0
wlan 11649024 0
and the modules installed in /sys/module look like
adreno cam_context_utils cs35l36_dlkm esoc_mdm_drv hid_magicmouse l2tp_netlink msm_drm nf_conntrack_netbios_ns ppp_mppe random snd_pcm tcp_cubic videobuf2_memops workqueue
adsp_loader_dlkm cam_cpas_hw debug_reboot eud i2c_algo_bit l2tp_ppp msm_performance nf_conntrack_sane printk rcupdate snd_timer ufshcd_core videobuf2_v4l2 wsa881x_dlkm
apr_dlkm cam_csiphy_core diagchar event_timer icnss libcomposite msm_poweroff nf_conntrack_tftp pstore rcutree snd_usb_audio ufshcd_pltfrm videobuf2_vmalloc xhci_hcd
arm_smmu cam_debug_util dm_bufio fb ip6_tunnel lkdtm msm_show_resume_irq oscar q6_dlkm rfkill spidev uinput vmpressure xpad
asix cam_ois_core dm_mod firmware_class ipv6 lm36011_module msm_vidc_ar50_dyn_gov overheat_mitigation q6_notifier_dlkm rmnet_ipa spurious usb_bam watchdog_v2 xt_quota2
battery cam_smmu_api dm_verity fscrypto kernel loop msm_vidc_dyn_gov overlay q6_pdr_dlkm rndis srcutree usb_f_gsi wcd934x_dlkm xz_dec
binder cdc_ncm dns_resolver ftm5 keydebug lpm_levels native_dlkm pac193x qcom_llcc_edac rng_core st21nfc usb_f_mtp wcd9360_dlkm
binder_alloc cfg80211 drm fuse kgsl lpm_stats nf_conntrack pci_msm qmi_rmnet sch_htb stub_dlkm usb_storage wcd9xxx_dlkm
block configfs drm_kms_helper gasket kgsl_gmu machine_dlkm nf_conntrack_amanda peripheral_loader qpnp_power_on scsi_mod subsystem_restart usbcore wcd_core_dlkm
bluetooth core_hang_detect dummy glink_pkt l2tp_core mbhc_dlkm nf_conntrack_ftp phy_xgene qpnp_rtc service_locator suspend usbhid wcd_cpe_dlkm
bonding cpufreq dwc3 heatmap l2tp_eth mhi_qcom nf_conntrack_h323 pinctrl_wcd_dlkm qpnp_smb5 sg swr_ctrl_dlkm usf_dlkm wcd_spi_dlkm
brd cpuidle dynamic_debug hid l2tp_ip module nf_conntrack_ipv4 platform_dlkm r8152 sit swr_dlkm v4l2_mem2mem wglink_dlkm
bridge cryptomgr edac_core hid_apple l2tp_ip6 msm_11ad_proxy nf_conntrack_irc ppp_generic ramoops snd sysrq videobuf2_core wlan
On the one that I built
lsmod looks like
lsmod
Module Size Used by
flame:/ $
and the built in drivers look like
adreno bridge core_hang_detect drm firmware_class ip6_tunnel l2tp_netlink msm_performance nf_conntrack_irc pci_msm qpnp_rtc rng_core spidev uinput vmpressure
arm_smmu cam_context_utils cpufreq drm_kms_helper fscrypto ipv6 l2tp_ppp msm_poweroff nf_conntrack_netbios_ns peripheral_loader qpnp_smb5 sch_htb spurious usb_bam watchdog_v2
asix cam_cpas_hw cpuidle dummy fuse kernel libcomposite msm_show_resume_irq nf_conntrack_sane phy_xgene r8152 scsi_mod srcutree usb_f_gsi workqueue
battery cam_csiphy_core cryptomgr dwc3 gasket keydebug lm36011_module msm_vidc_ar50_dyn_gov nf_conntrack_tftp ppp_generic ramoops service_locator st21nfc usb_f_mtp xhci_hcd
binder cam_debug_util debug_reboot dynamic_debug glink_pkt kgsl loop msm_vidc_dyn_gov nvme ppp_mppe random sg subsystem_restart usb_storage xpad
binder_alloc cam_ois_core diagchar edac_core hid kgsl_gmu lpm_levels nf_conntrack nvme_core printk rcupdate sit suspend usbcore xt_quota2
block cam_smmu_api dm_bufio esoc_mdm_drv hid_apple l2tp_core lpm_stats nf_conntrack_amanda oscar pstore rcutree snd sysrq usbhid xz_dec
bluetooth cdc_ncm dm_mod eud hid_magicmouse l2tp_eth mhi_qcom nf_conntrack_ftp overheat_mitigation qcom_llcc_edac rfkill snd_pcm tcp_cubic v4l2_mem2mem
bonding cfg80211 dm_verity event_timer i2c_algo_bit l2tp_ip module nf_conntrack_h323 overlay qmi_rmnet rmnet_ipa snd_timer ufshcd_core videobuf2_core
brd configfs dns_resolver fb icnss l2tp_ip6 msm_drm nf_conntrack_ipv4 pac193x qpnp_power_on rndis snd_usb_audio ufshcd_pltfrm videobuf2_v4l2
It appears that the one I built doesn't provide something necessary for the dynamic modules to load, and it also looks like the built in directory does not contain several dlkm binaries.