no its not. boosting salary and shares to convince someone to join is common. Its way harder to convince a new guy/girl to join with lower salary than to convince one of the already loyal internal employees to accept a lower payment and balance a cash flow.
You are way more invested into this and has spent a significant amount of risk, time, passion & effort that makes it easier to "convince" you to accept your current situation. Don't take it hard on yourself nor on the COO, if you were interviewing for a new company tomorrow, you'd negotiate as high as you could, the argument but our long lasting CMO is earning x won't really pay your rent.
<em>however</em> :
- A fair compensation model if cash is low is higher share. If you're earning 10 and COO is earning 15, then you should have 20 shares and she 5.
- Id reconsider working along with such a CEO that doesn't really offer a fair compensation model, especially someone who doesn't appreciate loyalty.
- Its also quite remarkable how a "Cofounder" has less shares than a newly hired employee.
That being said, if you are sure about the fact you're the backbone of the company you should renogotiate your terms. There's a lot of negotiation tactics for that, id strong advise against comparing yourself to the new hire, the "but he is that and im this.." puts you already in a bad box to start with. And in general people realise the importance of certain people once they're gone, preparing plan Bs wouldn't be dumb.