Fulham fan here again.
Slavisa was notorious for moaning about transfers (we were constantly speculating about his relationship with the hierarchy at Fulham). It's just something he does. Ultimately the fans will decide whether enough has been spent.
Just to clarify on an earlier post of mine, we didn't spend ridiculous amounts on our team (under Slavisa) UNTIL we made it to the Prem league because of FFP. Then only when we got to the Prem we spent big. But £75m was spent on 3 players who transpired to be championship standard (They are still with us). Whilst those who got us promoted were expected to be sidelined (The chairman's young son Tony Khan has done this twice now when we've been promoted), which basically meant Slavisa had to start building a team from scratch again (in the way he always does - tinkering). You don't have time for that in the Premier League (especially not with crap players).
I do reckon his previous public moaning was the reason he got so little time ultimately. Tony Khan doesn't handle criticism very well (see Scott Parker too). Hopefully your board won't take it so personally, because he's a top guy.