Ah, the old chestnut "What standard would Rangers or Celtic play in the English League".
Both their current teams would be championship at best but lets face it, they both have huge support and generate vast sums of money.
In the unlikely event that they were allowed to play in the English tier system, both their profiles would grow and doubtless their quality and, perhaps, their success.

At the moment, Celtic have players who help them piss the league at a canter but who would lets say just about hold their own or perhaps challenge for play offs.
From a Celtic board point of view, there is currently no reason to strengthen with better players and outlay larger sums of money on fees and wages.
Even if they did manage to attract top players, these would soon be dragged down to the level of their league as their potential would not be challenged often enough.
Celtic pull off a great result in Europe every so often but will never see them hit the heights of 1957 simply because of the lack of depth in their league.

It is not about these clubs splashing the money alone, though it is a very important part, it is about the standard of competition.

Until the likes of Killy, Aberdeen, Hearts, Hibs et al attract top players (highly unlikely) then Celtic and Rangers will always be open to (tongue in cheek) ridicule.

Up the buoys