If you ask me, Inflation is far more problematic than the Dark Stuff. Nevertheless, so far it remains the best explanation we have for observed phenomena ¯\_(ツ)_/¯
https://en.wikipedia.org/wiki/Cosmological_constant_problem
> Depending on the Planck energy cutoff and other factors, the quantum vacuum energy contribution to the effective cosmological constant is calculated to be between 50 and as many as 120 orders of magnitude greater than has actually been observed, a state of affairs described by physicists as "the largest discrepancy between theory and experiment in all of science" and "the worst theoretical prediction in the history of physics".
I was being somewhat tongue in cheek responding to OP, who was not specific about what they find problematic. The vacuum catastrophe is the area in physics where our explanations explain the smallest amount of our observations. We're very confident in our measurements and understanding at both the large and small scale, and there is essentially no explanation that anyone has any confidence in.
By comparison, observations of dark energy/matter are practically perfectly accurate. It's a single order of magnitude difference from expected observations. We have some half-decent candidates to explain them. Unlike magic, inflation is not a theory in search of an observation. The fact that we don't see inflation is what is so desperately confusing.
Without it, the Big Bang theory runs into major problems:
1. The Horizon Problem: The cosmic microwave background (CMB) has nearly identical temperature in all directions, suggesting the entire observable universe was once in contact. But without inflation, opposite sides of our universe would never have been able to “communicate” and reach this equilibrium.
2. The Flatness Problem: Our universe is remarkably “flat” (parallel lines stay parallel), which would require impossibly precise initial conditions without inflation.
3. The Origin of Structure: Inflation explains how quantum fluctuations during this expansion became the seeds for galaxies and cosmic structures we see today.