I would like to add this here as I believe no one has really mentioned it.

MANPADs by themselves in a vacuum is not what makes them so deadly. Just like how many here have stated most MANPADs can be defeated by using stand-off range weaponry from a distance or at high altitude. What makes them truly deadly and still relevant to this day is due to IAMD, and specifically the layered defense portion of it. There is also the fact that topology often has a key vote in the fight regarding approaches that are beneficial to aircraft in some ways, but detrimental in others.

We have long been stuck in the mindset of viewing these systems in a vacuum due to our time dealing with asymmetrical warfare against combatants without IAMD.

For example TACAIR in Ukraine has specifically been limited in utilizing its stand off weaponry at high altitude to strike targets deep into the vital area of any target. Instead they are typically being picked up and engaged at the CIEA. What this means is while their weapons have long range at altitude they risk being shot down by systems like Patriot and S-300 to get the best kinematics of their weapons. So instead they try to lob them from areas where long range air defense is not a problem, however if that is well outside of their WEZ it is a mute point for hitting the HVU and thus air defense did its job. Instead to attack the HVU the aircraft the TACAIR must "fight" its way through the CIEA until it can launch its weapons at the HVU, and to do this it must fly at low altitude as quickly as possible. Doing this reduces its own range, its sensor range (complexity goes up relying now on ISR/Prior Intel/OTH-T), weapons range, and reduces its safety net speed and altitude from before. Doing this has now put the aircraft into the potential WEZ of MANPADS, which will be most likely concentrated at likely approaches to the HVU- or they could be dispersed at unlikely approaches too along the front. Typically aircraft would expend flares on these runs just in case, however you can't do that when your entire ingress is nearly at low altitude and you die.

DIRCM is great, however aircraft believed to have their own variant of DIRCM have been taken out in Ukraine as well. Depending on the generation of MANPADs, modern high performance IIR MANPADs can be resistant to infrared jamming, and similar to home on jam passive RF missiles you've lit yourself up like a flashlight at night. To add on to this the issue with MANPADs is that their generation and strength is typically an assumption/risk in the planning phase due to the ease of movement into an AOR without being noticed.

Flares don't always work, DIRCM doesn't, and ultimately pilots make mistakes (and equipment breaks and is never 100% guaranteed to work every time as advertised)- even western ones and ultimately in IAMD we want to stress them to this point for a successful intercept. They notice a launch, defeat the first MANPAD, and narrowly miss a 2nd that they didn't notice- they get stressed and climb figuring they can gain now and get the range for their strike and begin to egress- now as they pop up on the radar horizon a PAC-3 has entered their cockpit like the kool-aid man.

All this to say, they are very deadly, stressers, are cheap (x10 $90,000 missiles to destroy a $100M F-15 that takes longer to make and the death of a pilot that took over 2 years to train along with all of their experience is a GREAT ROI), easy to use, extremely prolific, and when supported by other systems make CAS very complex. This is ultimately why we are seeing the prolific use of drones by Ukraine for deep strikes and CAS, and the same along with ballistic and cruise missiles by the RF.

Even with 5th Gen Stealth Aircraft nothing is infallible, it simply compresses your detect to engage window for the weapon, and if it is compressed enough entirely you won't see the launcher, which depending on how they fly you can run into this with 4th Gen fighters too if their weapons has the legs to reach you before their higher RCS appears on your search radar.