Skill’s compensator I think is slightly different term. I think the term ‘over biked’ is used to compare someone’s lack of skill / performance against others who are riding the same thing better on a ‘lesser bike’.
If you rode an XC loop on a 160mm ‘all mountain’ bike in a record time and beat your mates when they were riding XC bikes then you wouldn’t use the term. If you struggled to complete an XC loop on your ‘all mountain’ rig when they whipped round, then you would use the phrase.
Same applies to a DH run on an XC bike, if you beat your mates on DH bikes, you’d call them lame or ‘over biked’, if they beat you, you’d say I am ‘under biked’ and could be better on a DH bike.
However if you are riding something with more travel than what is required and using the bike to compensate on your lack of skills (i.e using you suspension to stop you crashing after coming up short on a small double) then your bike is a skill compensator – which isn’t a bad thing.
I found my full on 200mm DH bike gave me the confidence to try bigger jumps / drops which I now do on my 160mm / 130mm ‘play bike’.
However, I do also agree with stop making up phrases and just ride a bike.