I think it can be hard to define bespoke since there are so many ways tailors can make garments. FWIW, however, a lot of tailors use block patterns at this point, even on Savile Row. You still get a lot more freedom in bespoke, but in some respects, it's kind of like CAD/ MTM in that you start with an initial pattern (rather than draft something totally from scratch).
I actually think one of the main differences between bespoke and MTM is the number of fittings, not necessarily how patterns are drafted. You have more chances to get something right through that iterative fitting process.
Anyway, I think trousers can be made straight to finish. Not so sure it's a good idea for jackets given all the reasons stated up-thread. I also find it somewhat surprising a tailor would even offer it. Maybe he's had experience doing this and it's OK? I know some tailors don't do it because there's more emphasis on the fitting process than the pattern drafting (supposedly, this is more the case in Italy, but that might be one of those "regional differences" that gets overplayed on forums). Basically, some tailors cut the pattern a little big (sometimes even a little sloppy) and figure they'll just fix everything at the fitting. Which basically mean your "bespoke process" is all about the fittings.
I wouldn't do a straight-to-finish jacket myself, but I admit I'd be curious to see your results if you go for it.