Tyler has probably dealt with way more of these than me and that sounds dead right.
The issue with the arrestor tends to show up from first start with the motor feeling choked and not wanting to rev up. So, if it starts and runs freely from the outset, it’s less likely. However, I’ve seen symptoms similar to those you describe earlier on before the arrestor is more blocked. It’d be worthwhile taking the arrestor out and burning any residue off as that’s quick and simple. I sit them on a fire brick with another behind and apply a light oxidising flame from a map torch until there’s no soot remaining.
The valve strip down isn’t overly complex and there are instructions readily available from Stihl. These engines don’t like extended part-throttle usage, especially when run using the stihl 2-stroke oil. Not bagging the oil, I use it myself, but I find it needs a good proportion of the operation to be in the upper part of the rev range or things do gum up.
I’ve also seen the combustion chambers pretty filthy on machines that haven’t been given much full throttle use and, in one situation, gummed up rings. It’s not a difficult thing to fix, provided that the problem’s been caught early on. It can just require a gasket kit, a strip down, thorough clean and reassembly.
What tends to happen is the partially burned combustion products coat the surfaces. So, when the engine heats up and parts expand, some of the designed clearances are not available and the engine tightens up and won’t rev.
The higher performance 2-stroke oils work exceptionally well at providing lubrication at higher temperatures and duty cycles. However, if the engines don’t reach the designed temperatures sufficiently frequently you can end up with a sooty and sometimes tarry residue that prevents normal operation.