There is a lot to unpack here.
Assuming we're talking about the conventional deadlift, this isn't true. A lifter's leverages are going to play a huge factor here. I had a 500lb deadlift when I only had a mid 3s squat, mainly because I have a short torso and long limbs (with especially long forearms). I am built for the conventional deadlift, which means I am NOT build to squat. Someone with a long torso and short legs is going to be a monster squatter while having difficulty performing a conventional deadlift, which is why these types of folks tend to pull sumo in powerlifting.
Accepting my above statement as true, we again understand this statement to be true only in certain circumstances. In general, I find the conventional deadlift more a hinging of the hip movement than simply a squat with the bar on the floor, so I don't find that the barbell back squat has significant carryover to it. Chins and rows aren't bad, but if your grip is the thing holding you back, it sounds like you simply have a weak grip. This can be fixed with grip training, which (along with neck training) tends to be one of the most neglected areas of training. Most folks attempting to passively train grip (letting other movements in the workout do it), while those folks with a monster grip ACTIVELY train it.
As an anecdote, I've pulled a 650lb deadlift off the floor at 200lbs bodyweight, and I haven't performed a barbell row in years, nor do I ever go heavy on rows or chins. I go with very high volume instead. I don't find strong rows/chins necessary to build a strong deadlift, and attempting to use farmer's walks to build a deadlift seems disastrous to me (unless you're just practicing the pick-up).
Here is where I tend to be a heretic and say that, unless one wants to be a strongman or powerlifter, I see no real compelling reason to have the barbell deadlift proper in a routine. It's a pretty arbitrary movement, where plate diameter was determined as a means to prevent injury for olympic lifters on a missed lift, and in turn that plate diameter now determines the ROM of the movement. I like partial pulls, neutral handle pulls, odd object lifting, and a variety of other approaches.
I imagine this is because strong benchers are weighing upwards of/over 300lbs, which is a monster overhead press. It's an odd thing to compare their bodyweights in this metric, as I know of people that can overhead press their bodyweight while still not having great benches, because these people weigh 140lbs.
A strong presser will be strong at pressing. Mobility might limit their overhead ability, or simply a lack of practice. That said, body size can also play a role in benching ability, in the sense that a bencher with a massive belly can reduce the ROM of the movement, so there are a lot of factors at play.
As for your questions regarding how much time should be spent doing XYZ, it all depends on your goals. Decide what you want to do, then determine the best way to get there.