What is your experience when you have to use the QWERTY layout? Is it a frustrating experience or can you use it just fine given that Colemak is more similar to it than Dvorak?
If it's a Mac, Colemak is one of the pre-installed layouts, so if I need to work on someone else's computer I'll just enable it while I work on it and remove it afterwards. Otherwise I can manage, but it does slow me down quite a bit, and I'll have to look down at my hands pretty frequently. You immediately notice the extra workload though: Colemak is pretty low effort, but QWERTY just feels like finger moshing to me now.
I'm pretty sure it's possible to remain proficient in both, but QWERTY was sufficiently destructive to my hands that I use it as little as possible.
However, I rarely need to use Qwerty. It's less than once per week. The only times are when I'm in the UEFI settings on my laptop, or fixing my wife's computer. Any other time I have my own user, and can switch the layout to what I like.
Having an external keyboard also means that other people can still use my work laptop when needed (pairing etc)