grammaticality - Is "I've seen a lot (of them) using..." grammatical without the object?

During a conversation about programming, I meant to say:

I've seen a lot of programmers using that pattern.

I accidentally omitted the object and wrote:

I've seen a lot using that pattern.

For some reason that doesn't sound wrong to me. From context it is clear that I'm talking about software engineers without explicitly mention them, thus I don't need it for understanding. Quite the contrary, it would even be fine without repetition.

However, is that sentence OK without the object or should I use one of the following sentences?

I've seen a lot of them using that pattern.

I've often seen the use of that pattern.