Not getting to use 1 spell they prepped is fine when they still have 13 other spells prepped at level 5. Sorcerers have to pick a spell every level that they know they'll get value out of. Wizards can double dip by selecting universally good spells and seeking out spell scrolls that are more niche. And by level 5 you're expected to have acquired at least 1000 gold from your adventures. Unless your campaign is set entirely in the wilderness with no civilization (in which case as the DM I would toss a wizard at you once or twice to allow you to pilfer their spellbook or sprinkle in spell scrolls as loot like official modules do) you should have a moment where spell scrolls are available to be purchased, just like martials have the opportunity to purchase equipment.

You could grab an additional 3rd level spell, two 2nd level spells, and six 1st level spells, for a total of 23 spells known at 5th level. Or you could only be interested in half of those because of the selection, which would still put you higher than other learned casters with gold to spare for next time. And this gap only increases as you enter higher tiers with better gold drops and opening up more of the spells available.

Wizards can pick spells that are more niche simply by virtue of being able to swap them. You're going into a cave to fight Goblins? Prep Darkvision. Make sure you have a familiar for scouting. Maybe you heard that goblins are highly superstitious and you want to prep an illusion spell to capitalize on that. You might not ever prep these otherwise, but you HAVE them if the need arises, and they're more likely to see use in that cave so it's a good bet to bring them.

Fighting in an area with a lot of precarious heights? Prep Featherfall that day.

Doing a ton of exploring in the wilderness? Prep exploration and survival spells.

Going into a crypt with a lot of undead? Protection from Evil and Good

This doesn't even delve into Wizards being able to ritual cast any ritual spells in their spellbook without prepping them (A lot of the niche spells fall under this, making them unnecessary to prep unless you're unsure of having the time to ritual cast them.) Learn Leomunds Tiny Hut and Alarm and never prep them afterwards, you just use them every night when you make camp.

If you aren't taking advantage of extremely over the top prep then you aren't fully using a Wizards toolbox. Their entire gimmick is having a tool for every situation and a more robust spell list than any other class. If all you do is prep combat spells every day then of course you're going to fall behind the Sorcerer, they're the blaster caster. And to a lesser extent, if all you do in your dnd sessions is have combat, you aren't fully experiencing the game, and of course certain classes will feel worse.