To a certain degree, it can be a little pedantic as "What defines a #1 vs an ace".. etc etc. are the aces the 6+ fWAR guys? 5.5+ ? 5+?
Or, just the top 3-5 SPs each year regardless of WAR? If we take the 6+ FWAR - There's only 4 aces in the league, or 4 if you allow for leeway in fWAR ... Skenes(6.5), Skubal(6.6), Sanchez(6.4) and Crochet(5.8).
Are the #1s that arent aces in the 4.5 to 5.5 range? That list is Webb, Yamamoto, Fried, Brown, and Luzardo.
But, that type of system then discounts the guys that come up late, or come off injury and put up solid #'s on a per game basis but just arent there long enough to accumulate the fWAR. Is Schlittler a #1? Snell, Ragans, Woodruff, Megill, Lopez... all those types fall in there. Hunter Greene? Trevor Rogers...
There's probably some what to quantify it based on combined per game stats, actuall stats etc, but as we all know for SPs, staying healthy is huge.
But, to continue your eval of Gausman, I agree. He'd be a solid #2 on any staff in baseball where you'd also get the occasional flashback to the Gausman of the past like we saw with his CG not too long ago.
Really right now for starters the Jays are counting on Gausman, Yesavage and Bieber. Not the worst trio by any stretch and if they are all at their best, they can match Seattle's top 3. But when you look at the question marks and what ifs, you'd probably lean towards Seattle having the edge.