Yes I have played tower defense games, and you could say I know my way around videogames. I know what good enemy design looks like.
Again, I don't have troubles with demolishers, and I am aware of the things you said about him being "a good design", and my apologies if I wasn't clear. That's precisely his problem, its that all his purpose goes away when you pop him from afar, such a big monster taken down with ease, and every other zombie around it. The only times he causes any sort of trouble, is when a turret pops him, which you really have no control over, and it comes off as an annoyance more than anything, it's not like you missplayed and suddenly you lost your traps. With kamikazes, you know they're going to explode, they will explode on contact, they run fast, they're not just 1, they're also not very tanky, but they're fast, and if they reach your walls, its your fault. The demolisher zombie ticks before he explodes, meaning your turret can tap him and he still has time to reach your base with all that health, and you could never really react to that turret tapping him with all the confusion going on in a bloodmoon.
Alas, the only "troubles" I've ever had in A21 bloodmoon with demolishers, was a 2 time thing in a total of 62 days, first time out of negligence, we had a wall breached by the zombies and a demolisher entered, and one of my friends missed a shot and he blew up in the middle of our base, taking down a few wire relays but not much. And the second time, it was on the later days, we allowed him to explode and breach a wall.
All of this could be avoided if I didn't handicap myself by saying "we don't repair blocks during bloodmoons, only if they're broken". Because zombies still focus on 2 of the most damaged blocks, allowing players to spam repair them, which I didn't want to do this time around. On the other hand, spider zombies and cop zombies, are the only ones that consistently make bloodmoons interesting.
As for your spike example, I never said I didn't agree my friend, I really like the fact he stomps spikes. I am totally against an easy bloodmoon, thought that was obvious from the start. My issue, is that the demolisher doesn't consistently make the bloodmoon hard/interesting, unlike cops and spider zombies (mostly cops). He is just annoying when he explodes, not because I care about my walls being breached (I'm running parkour and run and gun, killing zombies on an open field is my comfort zone), but because currently explosions damage electrical components through walls. I can't tell you how many times cops sniped my spotlights or turrets and I'm forced to take them down or bait their shots, but that is dynamic and interesting, and also makes sense (you can see the windup, you can see the projectile, you can move away from your turrets, you can place your turrets behind cover, you can stun the cops before they puke..etc).
The demolisher falls flat on its face, simply because, unlike the other 2 special infected, his ability is not a consistent threat, or even an ability for that matter. Even if you do activate his explosion, you have time to gun him down, even when he's ticking (but you gotta be focus firing him from the start of course).
I said I like the that he is a big boy, but there is so much emphasis on his explosion, when its really just a random occurence that in this day and age of 7 days to die, is not even a big deal when you have so many resources and ammo, making it another bullet sponge (which I don't mind, but then again, it brings nothing to the table unlike the other 2). Demolisher is simply a newbie killer, by the time he shows up, he's not really a threat. I always take over a POI for my bases, and this last time we used a military checkpoint, meaning, concrete walls, catwalks, spotlights, single spike row around the base, nothing too strong, mostly just realistic. So imagine if we actually tried to make a proper bloodmoon base to abuse the zombies, or had a separate one with no regard to damages because f*ck aesthetics for that one.
Hence why I said, I would much prefer more zombie types, that swarm your base with different effects and abilities, and force you to pick VIPs and rethink weaknesses of your base based on what you have placed there. The demolisher is simply an overtuned normal zombie (which is perfectly fine), but somehow is a "special infected" because he can explode by getting shot in the wrong place? He could be a brute/bruiser, and have AoE on his normal swipes, dealing 500 per hit, on a wider block radius, that would be much more interesting and consistent, and also allow more to spawn.
And when I meant artificial difficulty, I mean that its just something they shoehorned in to give you some difficulty. I mean c'mon, it's obvious this design wasn't really thought through, his visuals make no sense and like I've said before, he's just a normal overtuned zombie that "might" explode. I would much prefer normal zombies to have explosive variants, rather than the whole personality of a custom modeled tanky zombie to be that he shines and explodes by the players demand (how many people actually know he can stomp spikes, I didn't until I started modding 7days lmao).
Right now, we only have 2 zombies (3 if you count the demolisher
) that make the bloodmoon somewhat interesting and dynamic.
Demolisher: Heavy breacher, minibosss, really dangerous to walls (should you focus on his physical aptitude and less on his explosion)
Cop: Sniper/Breacher, takes out turrets and spotlights from afar
Spider zombie: Jumps over defenses and forces you to either build a higher wall, or cage yourself to avoid it.
Honorable mention: Vultures, as they force to put sky coverage on your catwalks/platforms.
In the end, I would much prefer if they doubled down on the demolisher's physical attacks and make him a force to be reckoned with, with no cheap way of killing him, and also no cheap way of getting stuff blown up by things you sometimes don't have control over. I will note however, I do like that he makes explosives a danger to work with, but his weakness is still the same if you willingly pop it from afar, no explosives needed
In hindsight, it would be really nice to have those kamikazes have this particular strength. They won't pop from shots, but they will from explosions. Considering their faster movement and higher spawnrates, not being minibosses, it would be a good trade off (1 explosive for 1 explosive zombie).
Also I lose my track when writting really fast, so if I didn't mention some things, it's quite common whenever I'm brainstorming or discussing a topic. I automatically assume people understand what I mean with some things, when I should've been more specific. My bad for that.
. While you at the same time did not react to my argument above why the demo is actually a good design ( 
(I for example have to play SP for that). But whether you simply mine for ammo and shoot everything that moves or mine for cement and iron and build an intricate base with traps and pits and funnels and secondary positions and alternate positions, that is your decision.
