I feel like Voldemort with horcruxes, but plain Voldemort is less than Grindelwald.

The only advantage Voldemort had against Grindelwald was immortality

Yes, besides that Grindelwald is actually better.

And he's far wiser than Voldemort.

In my opinion, Tom Riddle only got that far due to his cunningness, which is not so similar to the wisdom Grindelwald had

Also his willpower to desperately cling to life at all costs.

Indeed

Meanwhile bada** Dumbledore being stronger than Voldemort and wiser than Grindelwald

Yes, stronger and wiser than both, he soloed Voldemort and Grindelwald separately.