I think the issue here is not the advantages or disadvantages of their scale.
Rather the chilling effect - the firms themselves (may be) slow to perceive the next iteration of consumer needs.
Startups on the other hand figure them out - and build a product.
The big fish/spiders, with their larger webs, sense the new upstarts and THEN build those features - and then go back to whatever it was that they were doing. The cycle then repeats.
As can be readily observed with the MS v Netscape battle over web tech (while called a browser war, my impression is that the browser was a proxy for getting a foothold in the server market).
Never mind that MS had pulled something similar vs Novell some years prior, by bundling a client with Windows and then marketing their Exchange server as a drop in replacement for Novell's Netware. Just set up a NT box in the server room, configure the PCs, and phase out Netware.
Rather the chilling effect - the firms themselves (may be) slow to perceive the next iteration of consumer needs.
Startups on the other hand figure them out - and build a product.
The big fish/spiders, with their larger webs, sense the new upstarts and THEN build those features - and then go back to whatever it was that they were doing. The cycle then repeats.