Celtic and English Again

[Peter &/or Graham]

On the lack of influence from Celtic in English:

Perhaps a comparable situation can be found in Egypt, which was
Egyptian-speaking for yonks, then Greek speaking for nearly a thousand
years, but now speaks Arabic with very little, if any, trace of either
"substrate".

Does this suggest that languages can indeed be replaced without great effect
on the invading language, if other circumstances are right, and that the
lack of influence from Celtic on English is not really so remarkable?

Peter