It's not an issue for me that different classes have different roles. It hasn't been an issue in any group, any game, for the past decade.
Is it an issue that 5e is often credited with doing away with roles, entirely?
"There's no combination of classes you need, play what you want."
Like, people are actually saying things like that. (I've been away from here a few years, I was genuinely surprised by that one - I know 5e did away with support for the 'tank' role almost entirely, and made in-combat healing
bad, but the idea that Wizard, Cleric, Fighter & Rogue are somehow interchangeable, I find bizarre).
Right. Point being it’s not “a garbage assumption” that the wizard will have a relevant spell. They may not always have the perfect spell, but they will almost always have a relevant or useful spell.
TBF, back in the day, when the magic-user started with Read Magic, and three random spells, and had to pick one to memorize at the start of the day, it would be a stretch to expect that spell to be useful in more than one encounter or challenge in the coming day.

Though, also, tbf, it'd've been a stretch to expect it to be useless in every challenge the day would bring.
Even as magic-users rapidly gained spells per day, the limitation of needing to memorize each spell was still significant, and the prospect of learning new spells was very much up to the DM.
5e, tho, with spells known picked by the player and increasing steadily with level, and prepared spells picked from that list daily, and prepared spells cast with slots
spontaneously, the chance to bring a good spell to bear in every situation is really pretty favorable. The best it's ever been, taking into account only spellcasting ability (wands & scrolls in 3.x/PF1 could really pump up the availability of low-level & situational/utility spells).