The issue in a nutshell is less that Terran is imba and more that Protoss design is a joke.
Lets look at this logically. Protoss Gateway units are purposely kept bad and everytime a Gateway unit ends up being good (old Chargelots) they get nerfed significantly, even if it wasn’t a balance issue (like it was when blink allins were overpowered in HotS) so Protoss HAVE to rush tech. Now for tech you basically have to rush Robo. No point in rushing a Stargate because Marines kill anything in the air that doesn’t abuse ledges. In fact Oracles are so bad at harass now that they’re not even standard anymore and players have to resort to banking 2-4 Oracles before even attempting to harass.
Meanwhile in Terranland Terran get insanely strong core units with borderline imba dps density that’s only balanced out via splash damage, very, very low skill set&forget siege units (Tanks, Widow Mines, Liberators) and have very strong late game tech in the form of upgrades such as EMP or Liberator Range or directly in units such as Battlecruisers and Thors.
They even get extremely safe expansions that literally require a dedicated army to kill in the form of PFs.
Now I’m not saying all of this is imba, it really isn’t. My point is that Protoss don’t have answers to 3/4 of this crap and have to brute force their way through really imbalanced scenarios, with the imbalance being directly related to hilariously poor Protoss design coupled with nonsensical nerfs that weren’t even made for balance reasons.
So Protoss HAS to be ahead of Terran by a base to contest, because Protoss don’t have real answers to a lot of what Terran can field in insanely strong timing attacks (or just by spamming Liberators or if a bio ball shows up with a Raven to disable your tech unit that was supposed to keep you alive, which is complete at utter dog crap Blizzard, nerf IM. 11 second duration is too long).
A Terran who allins is a Terran who is rolling the dice, if you fail your allin, yeah, that 3 base Protoss now has such a massive lead that they could let you park Liberators over the mineral lines and not care too much and that’s supposed to happen. Terrans need to get better at sc2 in general, they have all the tools they need to beat P and Z solidly in ANY scenario, they just need to get better at using those tools and safely snowballing their armies.