With thousands of people discussing char op for years I haven't heard anyone say here's a one level dip you must take or your character will be under powered.
I haven't either but that's approaching the problem from the wrong direction. I get what you are saying though.
The direction is most recently "Dip Hexblade 1 for all of its benefits with CHR Pc's and don't worry about any background, backstory or whatever just use its great benefits." While you do not have to do so, its clear Sorcerers and Bards gain IMMENSLY from a 1 level Hexblade dip, Paladins certainly do also, there are whole threads dedicated to it and every guide instantly changed when that class came out.
My position is sure, but you better have a good backstory and reason why the pact power continues to work since it a binding contract with dark entities, it says so right in the description of warlocks and hexblade in particular.
There are essentially 2 positions in the many pages here. One is roughly mine, that the DM might not allow it and you need to think about it and work it out in some way. I apply this in general to everything, it is a fantasy game but even within that construct there are some rules, both written explicitly and implied by the full text of the books, that give a consistency to the game.
The other is everything is irrelevant that isn't hard-coded into the actual rules under hexblade, if it isn't strictly forbidden then its allowed, its my fluff and any DM that would present any restriction on it is unreasonable and terrible and ruining my game. Everything is RAW, the only RAI is my interpretation, and no descriptive text matters, and if the DM says so F him.
Something like the Lance argument I am involved in is minor, I wouldn't allow a Lance to use dueling weapon style. To me its clearly a loophole in the rules to which a joke thread was around 4 years ago. I don't think that is what was intended by the designers (RAI) but I don't know, its clearly RAW. To support my position a photo was posted and an absurd example was made, that halfling on a dog could technically wield 2 6lb lances with reach and benefit from two weapon fighting style and dual wielder feat as long as the halfling was mounted, but could not even use a shorter, 6lb glaive. Its is RAW, but logically there is not consistency there, so I think that's absurd, but I also said if your DM allows it go for it. That's not really an argument, its just a different style. If you can get a DM to buy it good for you. Not all RAW is correct, there is an entire forum on that, and the errata comes out all the time.
But it is clear to me that many were suddenly struck by a bolt of creative inspiration when Hexblade changes came out, and then started to figure out how they could get around the restrictive text that is not actually presented as a rule. This happens all the time when in all games when something comes out that is just flat out better, very few just state "wow this is really good, borderline OP or at least build defining, I need to use this. I need to talk to the DM to work this out, the restrictions in the flavor text should give me a downside to this so I can use it as a hook with the DM." Instead they try to figure out how to sell it to the DM with no limitations, to force it upon the DM, and then get mad when they get shot down for it. All I am trying is to give big picture views, don't be surprised if your DM says no.
In another thread I made an assertation that an immobile iron golem makes no noise, I was told that since the rules for golems don't say they are silent when immobile then they must make noise so my assumption was wrong, if I as a DM decided that they didn't make a noise when immobile then somehow I was screwing my players. Well, RAW the rules don't say they are silent and appear to be statues when immobile, however in 38 years of reading descriptive text of golems in various modules (including the one discussed in the golem description) that's my opinion. I was then told my experience was irrelevant to the discussion. There is that type of player out there.