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A "Jack of all trades" can be relied on to do many different things. Most Americans will automatically fill in "but master of none", meaning that he does not do an excellent job in any of those things.

In basketball and other sports, a "role player" can be relied on to do his job consistently well, but not at the level of a "star" or "superstar".

"Solid", "steady", and "reliable" are adjectives. If used without other adjectives, the implication is that the person or thing's reliability is its most important feature. Most things that are perfect for a particular task have other adjectives that are more likely to be used if they are applicable.

Something can be a standby when it is ready for use. It is reliable, but if it were the best, it would actually be in use. Quite often it was in use but replaced, but is still good for the job, for example a kettle that has seen better days but still works well.

The Oxford Dictionary has

1.1 count noun A person or thing ready to be deployed immediately, especially if needed as backup in an emergency.

with examples

The tugboat is truly multi purpose, as it can lead oil tankers into port, repair petroleum pipes in the sea and act as a standby rescue boat.

Soup is a great standby, and we Scots are the best soup-makers of all.

The Cambridge Dictionary has

standby noun something that is always ready for use, especially if a
regular one fails.

with examples

Board games are a good standby to keep the children amused if the weather is bad.

There are standby generators but these usually only have to work for a few hours a year during power cuts.

I'd say "competent"

...acceptable and satisfactory, though not outstanding.
"she spoke quite competent French"

The adjective trusty is a good word to describe something that's maybe not necessarily the best of its kind, but you know that it's reliable because you've used it for so long that you can rely on it:

Having served for a long time and regarded as reliable or faithful

Example sentence (from the Cambridge Dictionary):

I did the entire three hundred miles on my own—just me and my trusty bike.

I think you're looking for "Safe" as in "The safe choice". Definition 2 here calls it derogatory, meaning 'Cautious and Unenterprising' but still 'Safe'.

The word "Journeyman" is often used to describe an individual who is reliable but not the best in their chosen profession.

From Meriam Webster:

An experienced reliable worker, athlete, or performer especially as
distinguished from one who is brilliant or colorful

Journeyman as Matt Coubrough suggested, for a person. If you need a word that works with things, try stolid.

From Oxford: Calm, dependable, and showing little emotion or animation.

Perhaps you're looking for a "workhorse" -- it describes a person (or sometimes an object) that dependably performs a task. It's often used in contrast to flashier beasts such as racehorses, who might win a single race and bask in that glory while it lasts, but may well lose the next race. The workhorse isn't the best (nobody rides around town on the workhorse, given the option!) but it gets the job done out in the field day after day.

Oxford: "A person or machine that dependably performs hard work over a long period of time."

I think the word could be "trustworthy", always reliable but doesn't matter on being the best or not.