To add to (and reinforce some of) the above comments....

You're not going to lose control because you detect a little bit of flex in the frame. And you're not going to snap your frame with the sheer force of your pedaling. ;)

Touring bikes are often made to emphasize comfort (and reliability) over stiffness. As a result, it shouldn't be much of a surprise that one designed for touring has a bit more flex.

By the way, I may have missed it but I couldn't tell what kind of butting (if any) you used when you built the frame.

Any more than 2.37 mm, and you are overstressing your frame. Structural failure is imminent.

I assume you mean what is called "lateral flex."

The tubes are designed to be strong, but also relatively light. The amount of flex is actually quite small, but you'd need ridiculously heavy and stiff tubes (or more reinforcements, which would also add weight) to eliminate all of it.

The whole "laterally stiff / vertically compliant" thing sort of real and sort of not. It's come to prominence because the higher-end frames are using so little material, and because different CF layups and designs offer some control over these characteristics. They'll use stiff BB's (e.g. BBright) and oversized BB shell areas, along with layups and more carbon, to maintain stiffness while keeping weight down.

The thing is, if you aren't slamming the pedals with 850w like the pros, then a super-stiff bike will be overbuilt for your uses.

just remember,

the more weight on the bike the more flex for any amount of force exerted. this is true for any type of flex, vertical, horizontal, twisting, or any combination thereof. or the direction of force.

heck, i can turn my '96 gary fisher welded steel, boat anchor, small framed, large diameter, rigid forked devil of a mountain bike into a wet noodle by tossing a couple of watermelons in the back when i go grocery shopping.

I may be incorrect, but I don't agree.

The frame will only flex more at the BB if and when you apply more power to the pedal, specifically on the downstroke. E.g. lighter leg + more power will flex the same as a heavier leg + less power. The flex is pretty much all happening at the BB.

Your bike's handling will change radically when you add weight, but the frame itself won't flex more because you have weight on the back.

put a couple of watermelons on the back of your bike. coast down a hill, with your feet off the pedals, a quickly flick your handlebars back and forth...you'll see.

I tend to agree with watermelon huey, going from overloaded grocery loads, it sure as heck feels like the frame is noodling....

Is the stiffness in one axis and compliance , in another, that is the design trick..

working it out with a builder, versus just buying something shipped
in from somewhere else , under some made up brand name
is another issue.. No dialog as to the riders needs change the design

throw in a demand that it be as light as possible , something has to give..

that is thin small diameter tubes that are less stiff , compared to adding
diamete ,,and/or tube wall thickness,
and Perhaps.. shape change..
Extruded and Hydro-formed aluminum is done frequently these days..

leverage of the rear rack mass does an effective job of bending the top tube

re shaping the top tube , is adding a cost , but , say oval, laterally wider.. ,
a large diameter tube rolled oval, would resist that flexing better ,

still be somewhat compliant vertically, in combination with the other 2/3 of the triangle.

Like I said: If you put a bunch of weight on the back of a bike (and higher up), your handling will change. (To be specific, the handling will become more responsive and the bike to wobble side-to-side.)

That is completely different than "frame flex." "Flex" refers to how much the bike frame twists and turns when you're applying force to it.

Your own example indicates it. Why would your bike flex more -- especially at the front -- when you're coasting on a relatively smooth surface and not applying force anywhere to the bike...?

Is "2.37 mm" part of the 78% of statistics that are made up on the spot?

as mark twain said "there are lies... damned lies... and then there are (78% of) statistics." (i'm taking a little liberty here).