In the business world it is, because going from 18% to 65% market share is much more than a 4X improvement. Market share progress is highly non-linear in cost/investment/strategy. There are network effects at play favoring a winner-takes-all.

A (truly) clever argument! Def seems like a stretch though, especially if you're hoping to save GP's comment by suggesting that this is what they had in mind :-)

No, that might be the word origin but not how it is actually used. Just like "decimate" nowadays does not require a factor 10.

So instead of "10x" substitute "by a large enough factor or margin to make a significant difference". That is totally true globally speaking. Locally, in the US, you could however argue that apple abuses it's iPhone market share to sabotage competition (e.g. streaming, webstandards,etc). That just means you should sue both not neither.

Decimate used to mean 10% less (1 out of ten gone), nowadays folks mean 90% or about so less (9 out of ten gone).