I bet that he regrets doing business with Softbank, yes.

An anecdote I heard (unsure if true) was that Softbank had strongly encouraged Adam to focus on growth at the expense of profitability to a much higher degree, shooting for the stars much more than he otherwise would have done.

If I was Icharus and someone else had given me wings and told me fly much higher, I'd have myself to blame but I'd still be upset and filled with regret.