I believe that the difficulty scoring points is reflected well in the league GPG, although the lack of PPs does hurt stars who tend to score relatively more points on the PP.
One thing that belies this supposed difficulty is the performance of some of the older star forwards over the past several years:
Sedins- Daniel's career high in PPG was at age 29 ('10) and his career highs in goals & points were when he won the Ross at age 30 ('11). Henrik's two best seasons in points were at ages 29 & 30, when he won the Ross in '10 and finished 4th in '11. Daniel's 76 & Henrik's 73 points in '15, at age 34, were good for 8th & 10th.
St. Louis- Obviously a late bloomer, but still... set career highs in goals & points at age 31 in '07 (5th in each)... two of his other 4 best point seasons were at ages 34 & 35 in '10 & '11 (was 6th & 2nd)... won the Ross, with career highs in PPG and adj. points at age 37 in '13.
Iginla- Won the Richard & Ross w/ 52G & 96P in '02 at age 24. His next best goal seasons were at age 30 & 33 ('08 & '11). His career high in points were at 30 ('08) and the other of his best 5 point seasons were at 29, 31, and 33 ('07, '09 & '11). The last two seasons, he's still averaged 60 points at ages 36 & 37.
Hossa- Topped 60 points each of the past two seasons at ages 34-36.
Sharp- Set a career high in points in '14 at age 32.
Datsyuk- His two best seasons were at ages 29 & 30 in '08 & '09. He continues to be consistently ~PPG into his mid-30s.
Zetterberg- Two of his top 3 adjusted point seasons were at ages 30 & 32 ('11 & '13) and he continues to be ~PPG in his early-mid-30s.
Players who were 30+ before end of regular season that finished top 15 in points [or PPG in brackets] since '93 (only time in top 15 at age 30+ is bolded):
1993: 3 Oates (30)... [12 Gretzky (32)]
1994: 1 Gretzky (33), 3 Oates (31), 4 Gilmour (30), t9 Andreychuk (30), t15 Francis (30)... [12 Bourque (33)]
1995: 5 Francis (31), t6 Coffey (33), t10 Messier (34), t10 Oates (32), t12 Nicholls (33), t14 Hull (30)
1996: 1 Lemeiux (30), 4 Francis (32), 12 Gretzky (35), t13 Messier (35)... [12 Oates (33)]
1997: 1 Lemieux (31), t4 Gretzky (36), t8 Francis (33), t13 Yzerman (31), 15 Messier (36)
1998: t3 Gretzky (37), t5 Francis (34), t11 Bondra (30), 13 Oates (35), t14 Recchi (30)... [9 Hull (33)]
1999: t7 Fleury (30)
2000: 3 Recchi (31), t8 Sakic (30), 10 Yzerman (34), t11 Roenick (30), t11 Shanahan (31), 13 LeClair (30)... [3 Turgeon (30), 12 Robitaille (33)]
2001: 2 Sakic (31), 7 Bure (30), 8 Weight (30), t11 Robitaille (34), 13 Guerin (30), 14 Modano (30), 15 Mogilny (31)... [1 Lemieux (35), 7 Fleury (32), 12 Recchi (33)]
2002: 4 Sundin (30), t5 Jagr (30), t5 Sakic (30), t7 Oates (39), t9 Francis (38), t9 Modano (31), t12 Conroy (30), t12 Shanahan (33), t12 Tkachuk (30)... [8 Bure (31)]
2003: 7 Murray (30), 8 Lemieux (37), t10 Modano (32), t10 Palffy (30), 12 Fedorov (33), t15 Mogilny (33)... [14 Jagr (31), t15 Alfredsson (30), t15 Sakic (33)]
2004: t2 Sakic (34), 4 Naslund (30), t7 Aldredsson (31), t7 Stillman (30), t9 Lang (33), t12 Recchi (36), t12 Sundin (32), 15 Jagr (32)... [1 Forsberg (30)]
2006: 2 Jagr (34), t4 Alfredsson (33), t13 Selanne (35)... [9 Forsberg (32)]
2007: 5 St. Louis (31), t6 Sakic (37), t8 Jagr (35), t11 Selanne (36), t14 Alfredsson (34)
2008: 3 Iginla (30), 9 Alfredsson (35), 11 Kovalev (34), t12 St. Louis (32)
2009: 4 Datsyuk (30), 8 Iginla (31), t9 M. Savard (31)
2010: 6 St. Louis (34), 8 Thornton (30), 14 Marleau (30)
2011: 1 D. Sedin (30), 2 St. Louis (35), 4 H. Sedin (30), 6 Iginla (33), t8 Selanne (40), t8 Zetterberg (30), 10 B. Richards (30)... [11 Datsyuk (32)]
2012: t7 H. Sedin (31), t10 Elias (35), t12 Hossa (33), t12 Thornton (32), t12 Whitney (39)
2013: 1 St. Louis (37), t7 Kunitz (33), t10 Datsyuk (34), t10 Ribeiro (32), t13 Zetterberg (32)
2014: 12 Sharp (32), 13 Thornton (34)
2015: t8 Hudler (31), t8 D. Sedin (34), t10 H. Sedin (34)... [6 Datsyuk (36)]
Now it's interesting to compare the seasons thru '99 or '00 with some of the later years. One can make some sort of decent HHOF argument for just about anyone who appears until about '03. Then in '03 & '04, we have the likes of Murray, Lang, and Stillman... obviously not even close to HHOF. The past few seasons have seen the likes of Whitney, Kunitz, Ribeiro, Sharp, and Hudler. None of these guys is going to incite protests when excluded from HHOF.
When you look at the combination of how high these age 30+ players finished, how old they were, and how good they were, it gives you some idea of the competition. The past 5 seasons don't appear especially difficult in this regard:
2011- St. Louis 2nd at age 35... Selanne 8th at age 40?
2012- Elias (35), Hossa (33), and Whitney (39!) making their only appearances in the top 15???
2013- St. Louis wins the Ross at age 37!?!
2015- Hudler (sole appearance) and both Sedins (age 34) in top 10??
Also, somehow we're supposed to believe the NHL has virtually impenetrable systems and the competition is way beyond that of 20 years ago... yet a 31 y/o Jiri Hudler led the NHL in ES points and an undrafted Tyler Johnson tied for third. Yeah, no... not gonna buy that for a dollar!