That's crap.
West Indies in the 1970s and 80s (Roberts, Holding, Garner, Marshall, etc.) might have been better than the 1990s (Ambrose, Bishop, Walsh) but they were still hardly shabby.
England had Snow, Willis, Old, Hendrick, Botham, etc. in the 1970s and Fraser, Gough, Cork, Caddick, Headley, etc. in the 1990s. Probably stronger in the former.
South Africa didn't even play in the 1970s and 80s and in the 1990s had class like Donald, de Villiers, Matthews, McMillan, Pollock, Klusener, Kallis, etc.
India in the 1970s and 80s had Kapil Dev and not much else and in the 1990s had Srinath and Kumble. Far better in the latter.
Pakistan in the 1970s and 1980s had Sarfraz, Imran and Qadir - in the 1990s they had Wasim, Waqar, Mushtaq and Saqlain. Better in the latter.
Sri Lanka had Vaas and Murali in the 1990s and didn't play in the 1970s and had pretty average attacks in the 80s.
New Zealand had Collinge (at home at least), Hadlee and Chatfield in the 1970s and 80s and Morrison, Doull, Cairns and Nash in the 1990s. Nothing in it.
Zimbabwe didn't even play in the 1970s and 1980s and had Brandes, Streak, both Strangs, Olonga, etc. in the 1990s. Hardly the worst ever fielded.
All-in-all, I'd say the 1990s was probably the strongest decade for bowling in history.
Err, there is hardly any footage of the 1920s and before - most of the best stuff starts in the 1930s.
There are countless pieces of evidence to suggest wicketkeepers were far more willing back then than today to stand-up to the stumps.