I've not been saying they're worthless - but at low levels (≤8) they are not as good as raising the attribute.
Not from my gaming experience and not from the math I posted the other day.
At my table, 6th level human variant fighter took Heavy Armor Master, Sentinel, and GWM. He doesn't always get 3 attacks per round, but he does when he action surges or drops a foe (or crits, but that's rare even with feinting). He tends to use the -5/+10 when he Feints. He has a +1 Greataxe of Giant Slaying (the latter part only coming into play in about 3 fights so far against Ogres), but having a +1 weapon is not unusual at many tables. The nice thing about a +1 Greataxe is that the damage (11.5 with Str and GWS) is about the same as the +0 Greatsword the PC was previously using (11.3 with Str and GWS). The rolled damage barely budged, but the player feels good about the extra +1 to hit.
So in those cases that he does one -5/+10 Feints and gets in 2 other attacks per round, his damage if all of them hits is about 48 points. Typically, 2 will hit and he'll do 23 or 37 points of damage (depending on if the one that misses is the +10 plus sentinel D8 damage one).
The Rogue (18 Dex with a +1 dagger, again same damage as +0 shortsword, but +1 to hit) is about 18 points of damage. However, he is more consistent because if his dagger misses, he'll often use the short sword in his off hand for about 14 damage. At +8 and +7, both attacks missing tends to be rare unless it is a fairly tough foe.
Even without a nova, with 2 attacks (or possibly 3 with a dropped foe or possibly more with Sentinel), the Fighter is still often doing 23 points of damage, more than the Rogue can usually manage. The Fighter is at +7 with two attacks per round, so he tends to do better DPR than the Rogue. Non-nova DPR works out for AC 10 to 18 as 18.42 to 14.02 for the Rogue (less if he misses and refuses to not use his off hand weapon in an encounter), 21.99 to 12.56 for the Fighter (break even is AC 15). However, if the Fighter drops a foe, his DPR increases to 32.18 to 18.38 (note, this is not 3/2 times the 2 attack damage because if he gets a critical, he does not get an attack for dropping a foe). And, if the foe's AC is high, the Fighter novas. So, he almost always out damages foes per encounter over the Rogue by about 10 to 30 points. That's what will happen if you have 2 to 3 times as many attacks per round for 2/3rds the damage per attack and 1.5 times the damage when doing a nova. Sorry, but Math 101. 4/3rds damage most rounds, 2x damage some rounds, 3x damage when doing a nova.
Would he do better if he took +1/+1 instead of Sentinel? Probably. OAs in my game tend to be a bit rare. He tends to get them when the foes try to disengage near the end of combat (and his Sentinel still allows him to OA). But not if he replaced GWM with +1/+1. DPR is greater for GWM than taking +1/+1. Illustrated that point for a variety of ACs earlier in the thread.
The only two PCs that come close to the Fighter in nova damage is the Lore Bard with Fireball or the Moon Druid with Conjure Animals. Sometimes they nova better than the fighter, sometimes they don't. The Rogue can do some nice damage with his magic dagger that the previous DM gave him (allows him to cast Moonbeam 3 times per day), but once the PCs got to level 6, the Moonbeam aspect of that item is losing a lot of its luster. He still uses it, but I've noticed a drop off.
So yeah, our players (correctly) think that the Fighter does the most encounter in and encounter out damage (typically 50% to 75% more than the Rogue does) because they just see him piling on the attacks, more so when he novas. And the party often takes short rests between encounters, so the Fighter is often able to nova. Yes as DM, I do sometimes have scenarios where that is impractical, but that is not always the case. If the players want to take a short rest, usually they can arrange to do so without getting attacked (although some other consequences might happen).
If they are buffing, the only buff they do not typically throw on the Fighter is Aid (or if they do, they do the level 1 5 point Aid instead of the level 2 10 point Aid because with Parry, Second Wind, and HAM, he mitigates a lot of damage and doesn't really seem to need a hit point buff).
