When Walter Smith came back, he signed Thomson, Whittaker, Naismith, Broadfoot, Webster and Gow directly from the SPL or with very recent experience of having played well in it.
Whether or not each of those signings were successful, they'd all previously played in the Scottish top flight and in that regard, they were experienced in Scottish football.
I think there's enough of a connection between Smith's signing policy and the success that came from that transfer window and the next few years after it. We've not been signing the best the SPL can offer for at least 5 years. Armstrong, Gordon and Griffiths (as better SPL players) would have previously signed for us or them - not just them. McGregor and Forrest have neutral enough names to think they might have been at Rangers in other circumstances.
Whether it's appropriate or not to say, we're never going to sign or keep the James McCarthy, Aidan McGeady or Kieran Tierney types but the other ones I've mentioned above might have had to choose between Rangers or Celtic rather than just go to Celtic in different circumstances.