It is not far off if we assume that Garp, who unlike WB was not sick on MF war, is most likely still one of the best haki users there are in op world. Reason for that is that only him and WB were equals to GR, and unlike WB, Garp does not seem to be a fruit user, ergo his lacking destructive ability is safe to assume to have been overcome by sheer massiv haki. Moreover Garp already was discribed as the Demon of the marines iirc.
Therefore i doubt that any other character, except Shanks, whos haki was already pointed out to be special, and mayhaps Kaidou who seems like a brawler to me (pure speculation though), has anywhere near the amount of Haki Garp once was capable of in the past, not necessarily in MF war anymore though.
Furthermore Garp made it pretty clear that he at least pretty much stood hugely above Akainu by saying to Sengoku he'd better keep Garp down otherwise Akainu would get murdered, although he pretty much came to his senses shortly thereafter,meaning not to betray/weakening the marines by such a deed.
I may be biased here, but for me only Garp was able to inflict any damage to Marco (prior to kairoseki, the harm he received during that time for me has hugely affected his fighting prowess in generel, since i doubt that someone that normally does not feel any damage, because of DF, has a huge pain resistance), therefore his fighting capacity, at least for me, is still hugely underrated.
Wait what? All i remember is him stating that he could not stay the strongest forever...shit its been a too long time, i think i should reread op.....
BTW i dont mean to state/present what i wrote as fact, just things to consider.
I think there are a few too many assumption in your analysis of garp.
1- him and wb were gold rogers equals. I dont think this is the case. If anything they were a little weaker, but if they were his equals, espically wb, roger couldnt really be the king.
2- garp's lack of df power is compensated by his haki. This conclusion doesnt need to follow at all. The man can lift up a several 100 ton steel ball and throw it with ease. That hakiless feat alone puts him in the top 20 fighters we know about. Give him emperor level endurance and make him the best hand to hand fighter in op and he could have no haki and still be the 3rd or 4th strongest in his hay day.
So obviously garp has good or even great haki, but he doesnt have to have amazing haki just because he lacks a df. Miahwk could have mediocre haki and he would still be mihawk.
Also, and this will be controversial, lets talk about garp's haki. Haki is willpower, and as rey explained to my horror, "not doubting ones self, that is power" and tons of fans claimed chinjoa is weaker due to his emotional state. So haki is directly linked to ones emotinal state and drive. What is garp's drive? What does garp have to fight for or strive to acomplish? Roger is probably dead his son doesnt seem too important to him and he let ace be executed so why would garp have a powerful drive? Espically in the war when he was actively fighting against ace living which we saw later, is not what he wanted.
So that is just food for thought, i am not aure i even believe the whole "stronger belife = stronger haki" that seems stupid, but i have heard it enough i figured it was worth the mention.
Oh side note, speaking of stupid haki uses, if luffy can run out of coa, why does he cover his whole fist in it for elephant gun when he only need to cover the knuckles? The black look is cool but a waste of haki.
Ok for wb's "i cant always be the strongest" the oppertive word is "always" or "forever" it is the same way a parent will talk when they have to do something for their kids
Kid "dad make me dinner"
Dad "you will have to learn to make it yourself, i wont always be around to do this"
The sentence proves the parent will do the task, but highlights the fact the child needs to learn. Obviously wb isnt telling his kids they need to become the strongest.
I think most importantly is sengoku, the man called the buddah would surely know he cant give wb titles he didnt earn for the sake of unit moral.
If you were a certain MMA fightee who recently got his ass kicked by arguably the best ever professional boxer, what would you rather hear going into the match to give you a better out look on victory
"That man is the world's best boxer, he could defest anyone on earth in a boxing match he hs no equal"
"That man is 40 years old hasnt been in the ring in 1 year and even then he did bad. He is great but he is beatable, he may have been the best at one point but now he is old, this is you time"
Napoleon said 70% of the battle is moral. If you wanted to motivate your soldiers, sengoku yelling "watchout the storngest man on the world is comming" "oh no wb has the power to destroy the world" that isnt helping your soldiers.
I will admit sengoku is only as smart as oda knows how to make him.... oda had wb's "smart move" coating his ships then putting himself in the center of an ambush. That is the equivlent of turning invisible, robbing a bank, then reappearing in the center of a prison. Oda failed wb there. If oda had wb do that same exact move, only pop up in the tri current and try to take ace back, that would be genius, could you imagine that?
Also there is the arguement sengoku kept his title to keep his men on their toes, but that is stupid. His fodder wasnt going to assume wb was their level because he was sick. It could only possibly help in the op world.