anyone regretting letting him go now that he is fulfilling some of his potential?

He had done very little until Nathan Brown took over tbh, you can't regret letting him go if you count the whole time he has been gone and not the year or so he's been playing well.

Brown or Sam - tricky.

Nope.

Regrets would be if Kevin Brown and Luke Robinson went on to become test regulars. Jon Sharp I think it was once touted them as "GB's Future Half Backs" or words to that affect.

Of all the players we let go Kevin Brown is the only one I wish we would have kept. And I've been saying it for years.

Nope.

Where would you play him now?

And would it have hindered Tomkins' development any way?

Brown is a better 3 than he is 6.

By now Brown SHOULD have been established as the Wigan 6. Sam has the ability to be 7 or 1.

In one word NO

Not in the slightest