The switch to the freestyle 2 was basically seamless. Switching to the advantage 360 was brutal, but I can tell you that i have not only fully recovered my typing speed but have even improved on my historical ability.
I used monkeytype.com for a couple years before the jump to the advantage 360 and still to this day, and you can see the deep trough my speed went through while i figured out the ortholinear layout and thumb clusters, and the new all time high records i’ve recently set.
Switching layouts (e.g. qwerty to dvorak or colemak) takes a long time to get back to your normal speed, but ortho/columnar vs staggered in my experience is something you get used to very quickly.
But apparently there is a huge variance in how quickly folks adapt, so I may just be lucky or have enough past experience with different keyboard shapes that it happened to be easier for me.
I've been using some kind of split keyboard for the past 25 years, last eight on a Kinesis. My WPM on a normal keyboard is ghastly.