High speed railway
Obviously you don't know much about railways or dynamics. High speed trains can take much steeper gradiants than lower speed ones, partly because they are so powerful (have to be, for the speed) and partly because their momentum takes them up with little effect on speed (kinetic energy relates to the speed squared). The new lines built for the French TVGs have such gradients, following the natural land contours, that some passengers complain of the up-and-down feeling - like you get with hump bridges on the road. Curve radii are also less of an issue as high speed trains generally tilt into the curve.
A Hyperloop train doing 800mph is going to be very restricted in its vertical and lateral curvatures to limit the centrifugal accelerations (despite tilt) given to the passengers, if they are not going to barf up their last meals.
It requires very specialised rails that have to be laid under very high tension and welded so that the result is seamless and can withstand large temperature variations.
You have just described standard track-laying practice these days. It is not special. Keep up.
It's also much more expensive to ballast because normal ballast doesn't cusion things well above certain speeds and turns into nasty pebbles instead of spikey lumps of rock.
Most high speed track is slab track these days. The effect you describe occurs with track movement and does not occur if the track is properly laid, properly drained, and has modern stock running on it. It is actually more likely to occur on secondary lines with clapped-out rolling stock running on it. Believe me, I am an ex-railway engineer and have had to deal with such trouble-spots on the track
Whether or not the hyperloop claims are valid, I don't know,
The low costs are fantasy.