How do I beat defense spam?

Defense spam is so hard for me to deal with. I'll be able to kill the opponents army, take the map, overdrive all my mex and produce out like 4 factories, but I can't ever break the enemy's defense. Usually I play jumpbots, which already has a problem with defenses. I try firewalkers, but they never seem to do enough damage and always end up getting sniped by phantoms. Sometimes, I'll make really large armies and push, but to no avail. It is extremely frustrating for me to play these very long games where I know I am advantaged, but I am unable to close out the game and end up losing to players worse than me because of such a cheap strategy. I am hoping that I can find some advice here in the forums to finally beat this strat that has been the source of many of my recent losses, and the cause of my frustration with this game.

Escalate.

New jack should make it a bit easier.

I watched a couple of your replays for a bit more context, and here's what I have to say.
1) Early game pyro aggression is really good for holding the player back and forcing them to build defenses, which uses their metal. Don't throw your raiders away on a risky factory dive though, because you need to be able to pressure the enemy around the entire map because...
2) *Defenses can't move*. They're very strong but only in their one spot. You had a game where you had 5x the opponent's army value, but spent ten minutes trying to take out their shield spam. Use that jumpbot mobility to go somewhere else on the map and wreck their economy or main base.
3) If you want to hit the shields *head-on, get a Tremor* or some Emissaries. Maybe even Shockleys.
4) Don't forget to build *radar*, this helps you pick out weak points of the enemy's defenses and army distribution.
5) RECLAIM! Your opponent is able to afford these defenses because they're picking up the pieces after the battle. Deny this to your opponent (remember, their standing army is smaller than yours) and you'll gain another advantage.


If you're at 4 factories (35 buildpower or 35 m/s) it's safe to facswitch to something with artillery like Astran says:

Cloakbot: Slings are cheap (plus get Iris for radar jamming against counter batteries).
Tanks: Emissary, or Tremor if they're really dug in.
Rover: Badger is okay, Impaler has fantastic range but low dps.
Lance: 1 shots almost everything, but sluggish, flimsy, expensive, and overkills like crazy.

Long games, phantoms, and creeping defences have been repeated annoyances for me as well. These days I like to switch to air if I have advantage in army and a reasonable map control. To arrest the phantoms I have to spam cheap raiders. This is the part I hate the most cuz it's micro-intense. If the opponent gets a shield ball with phantoms hiding there protected by a mix of whatever and they sling you from far away, I can't think of anything more disgusting than that. From my experience, cloaky is strong mostly because of those slings and phantoms. I don't feel knight is strong, although I sometimes see top players claim so.

Merlins I say, those things just tear up shields.

Well positioned Missile Silos can really break up Porky-Porc.

How do they do the defense spam? Do they meant to stop quick pushing or they meant to be actual porc?

I found recently stop pushing porc fail because people kind of stopped fight continuously, focusing on build a porc and artillery spamming. Because bertha nerf maybe.