I think the usefulness of either a vacuum or gutter guards depends a lot on the type of tree debris that collects there. In my case, I get a lot of dry pine needles all year long, stuff related to pollen activity in the spring, leaves in the fall, and long (4-5") pine cones any time a strong east wind blows out of the east. Some of the smaller stuff sits there for months, regularly wet by rain, and not necessarily dry when I get a good weather opportunity to clean it all out. Heavy rain tends to wash the pine needles toward the downspouts, where they collect and eventually plug the downspout, resulting in gutter overflow during a downpour. Part of my roof is two stories up, and I really don't want to be at the top of a ladder doing cleanout.
I get up there twice a year with the gas leaf blower, moving carefully along a couple of feet at a time, leaning away from the edge and being careful about stepping on anything but roof. For most of the way around, that blower blasts the gutter clean, right down to metal. Anything in there, wet, dry, clean, dirty, even any puddled water, gets blasted up and out. In most cases, those long pine cones initially get pushed along the gutter for maybe a foot, then mix with other debris and get lifted up and out. Occasionally, a pine cone or a twig pruned by wind will jam sideways, or at a downspout I'll encounter a mass of wet, rotted pine needles plugging the opening tight enough that the blower won't dislodge it. Then I have to shut down the blower, rest the end of the outlet tube against the gutter lip, get down on my side with the edge of a foot against the gutter, and reach down with my arm to grab whatever is causing the problem. It's scary, I'm almost 76, and I can see the time when I'm old and won't want to get up there anymore.
One problem with a vacuum is that it probably won't get close enough to get anything wet, or that wet stuff will just plug the tube. Also, without a (future option?) fiber optic connection for visual view of the gutter, one just hopes an adequate job has been done. Same for a long tube connected to a blower. Thus the success of standing on the ground with a blower/vacuum and long tube really would depend on the nature of what's in the gutter. YMMV, so to speak.