Asisreo
Patron Badass
The vast majority of monsters actually do have creative ways to tack on disadvantage on their targets. It's actually a bit unique finding monsters that don't have riders save for humanoid enemies and obvious brutes.Even then, it is a borderline case IMO. And although some monsters have means of imposing disadvantage, the vast majority of them don't.
Let's take the AC 15 goblin vs. FB with a +5 spellcasting modifier. This means there is a 55% chance to hit (10 or better) which yields 3.3 DPR.
With disadvantage, this drops to 1.6775 DPR as the probability of hitting drops to just over 30%. But even assuming disadvantage both rounds, this is 3.355, just a hair better than using TS to remove disadvantage and casting FB on round two (3.3).
This is what I mean by marginal. TS+FB is 0.55 points worse than just casting FB twice with disadvantage. Tack on giving the enemy a fear turn to attack and concentration, it is a poor choice.
Another common problem is that alot of creatures are resistant to firebolt. Maybe not at level one but if a campaign isn't a humanoid only campaign, it's likely you'll come across one. And swimming enemies count since they want to fight exclusively underwater unless dragged out.
Ray of sickness still applies the rider. Also, poisons in the DMG give significant combat effects where them hitting is more important than damage as well (having a character paralyzed).
The point isn't that true strike is good. The point is to find applications for it as written.