I played Pathfinder 2e briefly, where base Rangers have no pets or spells. There are no formal subclasses as in 5e, but the feats generally fall under thematic categories (as in the chart below), and many have prerequisites, so you often end up with implicit subclasses; even if you don't have to fill out a given feat tree, or theme, you're usually leaving yourself weaker. For example, if you get an animal companion, you're practically obligated to take the upgrade feats to keep your pet viable in combat.
Anyhow, I'm not arguing that Pathfinder 2 solved this better—I really didn't enjoy having to sift through all those feats. But I figured I'd drop the chart to show the sorts of functional areas a optional 5e Ranger might want customization options for. As
@Charlaquin pointed out, the Warlock model is kind of like this, with Patrons being the thematic subclasses, Pacts being a hybrid between subclass & class feat (distinguished by being
mutually exclusive), and Invocations basically being class feats.
Maybe you could give an option to drop spell slots from the Ranger and instead provide Invocations/class feats (what would those be called for a Ranger, anyhow? Specialties?). You could even replace particular subclasses like Beast Master that way (with a basic pet plus some upgrades, so it can grow in power over time). Some Specialties could even provide individual spells (or functional non-magic equivalents), just like some Invocations do, usable at will, per rest, or what have you.
(Hm, totally off-topic, but now I am thinking of a Twofold Pact Invocation for Warlocks, where you could get a familiar and a book of shadows...if you really wanted to spread yourself that thin.)