Building your own team buys you long-term retention of knowledge. The engineers internalise your customers and your data model over time, and that accumulated context remains with you. The price shows up as time and rigidity: vue vs react filling a senior role takes months, ramping up adds several more weeks, and the cost continues through the quiet quarters.
Project outsourcing means an external team owns the outcome: they staff the project, they manage the process, and the provider carries the staffing risk. The model works when the outcome can be described and you have a decision maker with time for it. It works badly when nobody on your side owns the product, because an external team is not able to invent your business rules.
Hiring individual contractors falls in the middle: you rent capacity while keeping the planning and the management on your side. It moves quickly — a matching profile is often available far sooner than a new hire — and it winds down as quickly as it ramped up. The trade-off remains that your technical leaders have to have time for code review and offshore software development planning. Without strong internal leadership, the result is paying for effort with no owner.
Most of the time, these models are combined. A common pattern puts architecture, product decisions and core domain code inside the cross platform app development company, while an outside vendor handles the parts that are bounded and specifiable. The principle is easy to state: hold on to the parts that are hard to re-learn, and outsource the well-trodden work.
A few questions resolve most of these debates. To begin with: is what you are building the product itself, or a cost centre? Then: for how long does the work continue — months or years? Last: who answers the phone at two in the morning when it breaks? Work through them with real answers and the right arrangement becomes obvious.