"drastically better" is a correct and usable phrase in written English.
You can use it in any context where you want to emphasize an improvement or a change. For example, "The new design is drastically better than the old one."
Yonkers's fiscal straits are not about to get drastically better.
Republicans have better prospects of picking up the six seats they need to regain the Senate – but not drastically better.
Japanese competitors and young entrepreneurial ventures prove every day that drastically better levels of process performance are possible.
While Shumpert was leading a defensive revival, it was drastically better ball movement on offense that let the Knicks open a wide lead.
They have a chance to be drastically better, but in conversations with team officials, the expectation for improvement is tied to health, not underachieving second-year players.
The area of design optimization is where the performance of a design can be made drastically better than an initial naive implementation.
I thought when she went in, the dynamics in the back changed drastically for the better.
But the situation on that front has changed drastically for the better in recent years, because we're now achingly close to achieving a renewable-energy revolution.
Regular people got into it, and things changed drastically for the better.
The truth is that if we really care about animals, we must take steps to drastically reduce or, better yet, completely eliminate our consumption of animal products.
He played for four teams — the Dallas Mavericks, the Phoenix Suns, the Nets and the Knicks — and made each of them better, sometimes drastically so.
