From the standpoint of evolution science as it relates to the question:

Evolution definitely is a process, but it's not a smooth process. Essentially, although there certainly is a degree of crossover, the major visible changes that deliniate the emergence of a new species tend to happen relatively quickly in response to an event.

The event is generally a near-extinction or a group isolation.

In the event of a near extinction, the survivors all have a particular survival trait, and probably a handful of other similar traits as well, and due to the small population inbreeding occurs, and functional iterations of the available genetic material "pan out" as a new species that's noticably different from the old species.

In the isolation event, this is generally the same except for the requirement of a particular survival trait. An isolated group of a species inbreeds, has a lot of deaths and then a new species with exaggerated traits that were common to the isolated group and not problematic in an inbreeding scenario, emerges.

So rather than seeing people get taller over time in the fossil record (this has happened noticably in the modern world but it has a lot less to do with genetic changes than with dietary changes and generally more widespread availability of nourishment), we see a population stay mostly the same, then "suddenly" change, or die, or a new variant appear in one place.

All evolution is slow, but this is very fast compared to what people think of as evolution minus the near-extinctions and inbreeding. Which are really the primary drivers of major evolutionary changes. In the fossil record, most of these new and visibly distinct types appear near-instantly. Finding links and "crossover" examples is much rarer than just finding a new but distinctly similar species.