I'm A Banana
Potassium-Rich
The Thief Archetype has the following third level abilities:
Fa s t H a n d s
Starting at 3rd level, you can use the bonus action
granted by your Cunning Action to make a Dexterity
(Sleight of Hand) check, use your thieves’ tools to
disarm a trap or open a lock, or take the Use an
Object action.
S e c o n d - S t o r y W o r k
W hen you choose this archetype at 3rd level, you gain
the ability to climb faster than normal; clim bing no
longer costs you extra movement.
In addition, when you make a running jump, the
distance you cover increases by a num ber of feet equal
to your Dexterity modifier.
Would removing them and allowing a NONCOMBAT feat be "balanced"? To me, these seems pretty much the equivalent to a feat with three situational bonuses (two involving movement and one allowing an additional option for your bonus action).
Feats are generally more powerful than individual subclass abilities. Subclasses are largely in the realm of "this is worth about 4-8 points of damage per round, or isn't combat related." A feat can be quite a bit bigger - even a "+1 to attack and damage rolls" is generally more powerful than most subclass abilities.
So it would be an upgrade. By a bit. Not, like, a HUGE amount, but a bit. Noticeable when compared to other subclasses (if you had an assassin, they'd probably be jealous, for instance).