The problem with Shaheeds and other slow air like them is they're not substantially different to the type of vehicle which would be needed to intercept them.
So a stockpile of Shaheeds can be largely countered by launching something very similar provided you can detect it. You could very much imagine having a vehicle which can simply leave the payload behind for better air speed when used in interception mode.
This is quite different to most conventional missile threats where the time between detection and interception, as well as the performance characteristics, necessitates extremely high performance interceptors.
An analogy would be that you can hit a baseball with a bat, but not a bullet even though they're both just ballistic projectiles.
Interceptors being more expensive is a big problem. The only solution I can think of is ground-based lasers, which cost a few dollars per shot. If they can be protected.
Other than that, you either need the X-factor of intelligence and air superiority, which bypasses the problem by taking out bottlenecks like TELs and supply chains. Or, have more industrial production. If you have neither, you're in trouble.
A mostly independent thing countries can do is have better home-front resiliency, which is a kind of defense in depth against suicide attacks. Taiwan needs this. Get everyone a bomb shelter.
> Interceptors being more expensive is a big problem.
Yes, but they do not have to be. Shaheeds are slow, easy to detect and track and not maneuverable. They could be intercepted by very cheap short range systems.
What makes interceptors expensive are requirements to counter stealthy, maneuverable targets with very high success probability (i.e., when you consider a leaker to be catastrophic). Nether of this applies to current UKR threats. At least not yet.
Ample footage from Ukraine has shown that drones are very effective at getting into shelters, foxholes, and other enclosed spaces. Doesn't even have to be all that powerful of a boom, just enough to rattle everyone's cages enough to take them out of the fight for a little -- the next wave of drones will finish the job.
On paper, shaheed tier drones can be upgraded with better compute to fly much more complex (i.e. close terrain hug) which exponentially drops chance to intercept by forcing defender to increase/scale IADs density/complexity. Analogy cruise missiles -> LO/stealth cruise missiles with more complex compute and flight profiles, they're still subsonic and "easy" targets when detected, but make detection hard because scaling detection = scaling more nodes i.e. Same # of munition requires #^2 sensors to detect. Another analogy is urban tag, instead of slow player screamingly loudly at fast defenders, drone is sneaking to target quietly and defenders suddenly needs more eyes for same catches, perhaps not affordably more.
IMO the _current_ problem with subsonic / shaheeds tier munitions, at least the one's being being used is they seem to have very basic navigation capabilities field by forces that don't have ability to plan better missions. VS defenders being supported by US/NATO with high end ISR that dramatically improve intercept planning/chances. Again, IMO the latter is what makes or breaks, affordable theater level shaheed spam. These are glorified mopeds + smart phones. On paper most countries can have 100,000s of them. But to use them effectively and even _more_ economically, need highend ISR+killchain to employ fraction of munitions (or some other platforms) for initial SEAD / dismantle IADs and eliminate future intercepts. AKA closer to US/PRC tier of C4ISR which will ramp into another gear once mega-constellation based. Which is out of reach for most countries, unless they strategically align to "unlock" "smarter" munitions.
So a stockpile of Shaheeds can be largely countered by launching something very similar provided you can detect it. You could very much imagine having a vehicle which can simply leave the payload behind for better air speed when used in interception mode.
This is quite different to most conventional missile threats where the time between detection and interception, as well as the performance characteristics, necessitates extremely high performance interceptors.
An analogy would be that you can hit a baseball with a bat, but not a bullet even though they're both just ballistic projectiles.