Thanks for elaborating a bit more, Edington. I think that the solo sequences could differ in time because they are played over different progressions, having different length.
Look at The Writing in the Wall. Adrian is soloing much longer, because that piece is much longer (apparently it was thought that the length was fine). Making the Dave piece longer because he needs more solo time is not a purpose on itself. The purpose is having a good song in which the pieces should have a good balance, in length. The solos are secondary. Two solos of such length would feel over the top. Not important: Dave's solo is done over less variation of music than Adrian's which features more chords in the progression. Solo it would feel very weird (and monotone) to have Dave's piece that long.
Interesting to note that there are two song halves in Death of the Celtes and that a solo connects these. So, does Adrian start his last solo when the second half of the song starts? I never heard it this way, or thought like this, so I'd like to check it out. In fact it has been a very long time since I played the album.

(just taking a long break for some reason; it's not that I don't like it)