Insisting on this extremely literal, rigid definition of the term "1st line Center" as Top-30 scorers in the league because there are 30 teams definitely seems pedantic to me.
The easiest case of where this holds little water as a useful benchmark, is the Cup Champion Penguins, or a team like the Capitals, or the Stars or Bruins. They've each got TWO Centers who fall within the "Top-30" centers in the league for scoring. I'd suggest Crosby/Malkin/Backstrom/Kuznetsov/Seguin/Spezza/Bergeron/Krejci likely fall in the Top-30 Centers in the league by pretty much any metric you might reasonably apply. At which point you're effectively throwing out the "30 teams in the league" figure as pretty much arbitrary. The fact there is a set of 30 teams is largely irrelevant to your definition when some teams have multiple instances of #1C, and others have none. You're already conceding that the number of teams doesn't really have any direct correlation to the number of #1Cs in this arbitrarily rigid definition of #1C. It's not one #1C per team, which is the only reasonable case in which the number of teams would matter.
It's not really a big step further, and is actually a lot more precise to start talking about players that would be reasonably projectable as a #1C on a good team.
When you look at the Top-30 Centers in the league, you also have to subjectively draw some sort of line on for instance...guys who aren't even full-time Centers - guys who spend a noteworthy amount of time on the Wing. Where's the rigid line on that?
It's the NHL. It's full of blurred lines and subjectivity. There's an arbitrary quality to any definition of "#1C" you can reasonably come up with. Basing that arbitrary line on the number of teams in the league, when there isn't a relevant and even distribution is where you may like to draw your line...but it's still arbitrary and subjective just the same. Picking a cut-off number from an at best, tangentially related data set doesn't make it somehow definitive, or completely objective in any meaningful way.
As far as Dubois and Tkachuk go...
For me, Tkachuk is a guy where it's really hard to imagine he won't find his way onto a team's top line sooner or later...playing alongside whoever their best forward is. His style of play and ability to find amazing chemistry with a variety of types of high skill puckhandling players makes him extremely well-suited to play with a teams "#1C" or "best forward". That's where i see his best value fit. What i don't see as much with Tkachuk, is a high likelihood of him being the absolute anchor of a Top Line, or maybe not even a Second Line. He's an oddball sort of "complementary Top-3 Forward" for me. He's like a super-hotrodded version of your classic "complementary top-6 winger". Looks and plays like a grinder, but under the hood is the supercharged vision, smarts, and puck skills of a 1st line talent.
Whereas Dubois is a guy who looks to me more likely to really anchor a Top-6 line as the go-to guy...it just may not be the "Top Line" per se. His skillset seems more conducive to really carrying a 2nd line if he
doesn't end up as a top line forward. Some of that may depend on where he ultimately settles in position-wise as well. As a Winger, i like his Top-line upside more...though the versatility of playing Center is very enticing and adds value to his overall upside for me.
I think your point about a 60pt low-end 1st liner vs a 55pt high-end 2nd liner might be sort of getting at the meat of it though. In today's NHL...the notion of "1st/2nd/3rd" line is becoming completely blurred anyway. You get duos and depth. Your 2nd or 3rd best forward is as likely to be anchoring a separate line of their own, as they are to be actually playing with your 1st best forward on your "Top Line".
That's where you get stuff where you might have a 55pt high-end 2nd liner who plays there even though they could be a 65pt 1st liner...because you've got another guy who can be a 60pt 1st liner, but only a 45pt 2nd liner. It's all very subjective and situational.
The NHL is just not a rigid definitions league...categorizing players is messy, multifaceted, and highly dependent on situation.
