There will be a difference. Cobb OTS is very tame, and not vehicle specific. Adam can tune you based on your driving habits, your wants and needs, your specific fuel available, and optimize overall drive ability. Personally I would wait until you decide to go to Stage 2 to opt for an E-tune or Pro tune, but if you're going to get the lifetime tune anyways then he will just redo it once you get an FMIC and go to 2. This car can have alot unleashed just via tune, but the "staged" upgrades will help increase efficiency and longevity and reduce workload on the turbo and engine etc. There are many tuners available as well and some with other flash tunes a little more aggressive than OTS.
That's my two cents. And also a word of caution, be careful what you read and don't take all posts for truth. While some may feel Stage 2 with a pro tune is the "best choice" as you said, everyone has their own motivations for what may be the "best choice." Be it their budget, bang for buck, value vs cost, HP per dollar, engine life, drive ability, efficiency, road or track etc. So yes while SOME are under this "Etune Stage 2 or bust" mindset, I would most certainly not say "most people on the forum" have concluded as such.
So ya that's my Monday morning little blurb. Again just my opinion, which as I've cautioned, is not really worth anything on its own. Research and take in all there is to take in
PS. Nice to see more from Canada. There's some Facebook local groups if you aren't already on them!