There is no such thing as "W2 contractor?"
W2 = on payroll as their employee
or;
1099-Misc = your client, the Supplier, hired you as your own company, even if that means you are a subcontractor to the "Supplier" that has the higher level contract to the common end customer
When you are an employee of another entity, you are no longer an independent business. That means none of the expenses associated with that job are you business expense and there is no QBI, since there is no Sched C tax return for your "business" operations. At least, not for the job for which you are now hired and paid through payroll as someone else's employee.
An independent contractor cannot participate in any retirement plan offered by any other entity. You would have to chose and set up one of the IRS plan types that qualifies for you as your own business.
As an Employee, you would be qualified for whatever your Employer offers and on their terms, and no longer qualify for an independent business retirement plan, unless you also have other earnings that are not through an employee relationship but are still operating as your own business. You can have both types of work: an employer might not require you to work only for them, which allows you to work as an independent contractor to other businesses and you realize you have the time and resources to cover both types of work.
So, to summarize:
W2 = employee
1099-Misc = running yourself as your own business
