Agree but I think we need to be more precise about what meaning bigger is, without just saying "we are bigger" as it is open to interpretation and is ambiguous.
If we go back over the past 60 years, Celtic are the bigger club. Trophies galore (yes in a 2 horse race mainly, a 3 horse race when Aberdeen had their Fergie time and a one horse race when Rangers went bust) but a Euro Cup winner and a Euro Cup finalist in 3 years late 60's put them on the map.
But since the last 15 years despite still being the dominant side in the country, the club (and the league as a whole) have been going backwards both on the pitch and financially off the field, failing to make the CL qualifying rounds year after year.
And this is where City have become a bigger club. Both on and off the pitch. Matching Celtic's European Cup / Champions League record of being a winner and being runners up over a 3 year period, reaching the knockout stages for 11 years running on the pitch and going off the scales financially into a new stratosphere off the pitch.
Added to that, the rate of which City's world wide support has grown where as Celtic's will always remain as it is with Irish expats keeping the faith (literally) in all 4 corners of the world and that is why City have over taken Celtic in every aspect of the Football club