Hmmm.... now that's a naive statement...
How do you succeed in becoming a stronger competitor when you sell out a good proportion of your inventory to the market leader and you have no clear strategy, nor market-leading ad platform to entice new blood?
All G need do is to ensure they retain your ad slots by giving you good payouts to start with, until lots of savvy Y advertisers realise exactly what's happening and slowly start to desert in favour of a single advertising platform (G) which allows them to appear on Y too!
Then G ... slowly decreases the revenue of the clickthrough earnings until Y realises they are in no man's land with 50% loss of advertisers and an ever decreasing income from G...
I guess this is similar to many 'factoring' deals - where a company is desperate for invoiced funds to be received on-time to keep cashflow healthy, so they get some 'help' from a factoring company (for a small fee like 10-15% of total invoice).
Only it's usual for the company to become reliant on this immediate cashflow payment on invoice due date. This means the company can't then find enough spare funds to get out the deal and support the business, even though they know you are throwing even more money away in the meantime in fees....
Good luck Y... your advertiser numbers could well be going the same your share price is...
Then there were 2.... ?