Souness was never in Celtic, he was with Rangers. The thing is,
he was the one who took over Liverpool after their heydays in the
80s, and preceded over Liverpool's downfall in the league. At clubs
like Galatasary and Benfica, he didn't win them the league.
Southampton sucked until him too, and Rangers was the exception,
but only because Rangers was already strong before he came
in.
Souness may not be a bad manager, considering he managed to keep
blackburn in the EPL, but keep in mind he is not the right manager
to lead a big club like Newcastle. Newcastle flirted with
relegation last season, and this season, depends too much on
Michael Owen. Without Owen, his team loses most of the time. His
faith on Bramble and Boumsong is a mistake. They constantly makes
mistakes, and only Shay Given is keeping them above the relegation
zone. Without Shay Given, Newcastle will probably be competing with
Sunderland for last spot in the EPL.