I don't see much disadvantage. It's not like Tesla is designing and manufacturing the batteries they use all by themselves. Sure, they have input --as Boeing has input w/re GE engines.
Given that Tesla will be charging for their networks, it's not an advantage over other charging networks, so overall it'll be a non-issue. Having dealerships does grant the traditional MFGs some advantage but that may erode in the future if dealerships become less necessary in helping the sales of cars (ie. become more on-demand fleets). ICE car MFGs also have _capacity_. Tesla does not have the capacity right now.
Tesla designs and manufactures battery packs. GM is on record saying that it took them a long time and a lot of money to develop the battery pack for the Bolt.
GM didn't develop the battery pack for the Bolt. The battery cells, battery pack, charging systems, motors, computers and infotainment systems in the Bolt are all designed and manufactured by LG Chem.
Tesla uses Panasonic cells to make their batteries[1]. I'm sure Tesla has some circuitry/electronics to control the cells, but it's not like the key battery technology is all Tesla's.
The Gig Factory allows Tesla to ensure they have enough batteries for their car fleet so that they don't suffer from shortages as other MFGs put a demand on suppliers.
Given that Tesla will be charging for their networks, it's not an advantage over other charging networks, so overall it'll be a non-issue. Having dealerships does grant the traditional MFGs some advantage but that may erode in the future if dealerships become less necessary in helping the sales of cars (ie. become more on-demand fleets). ICE car MFGs also have _capacity_. Tesla does not have the capacity right now.