I don't think so.
As I said... I think Bergeron and Marchand can play with just about anyone.
And I also think there's at least some evidence to suggest that Beleskey-Krejci-Pastrnak could also be a fairly effective line.
From what I remember of Beleskey-Krejci-Pastrnak last year, yeah I think they're a perfectly good line, as is Marchand-Bergeron-whoever to your point. But is that really the best use for those guys, and what's best for the team moving forward? To me, we've already seen exactly what happens there, especially since there doesn't appear to be D help coming...it's a playoff miss. And I'd venture to guess that's why they ended up moving Eriksson alongside Krejci for most of the season anyways, because that top 6 wasn't strong enough to compete with their counterparts.
Beleskey replacing Eriksson was and is a downgrade, and if you have Backes at center, that means we're starting a rookie alongside Marchand/Bergeron, which while okay, is still a downgrade from Seguin, Recchi, or even Reilly Smith being there in the past. The point being, Backes at 3C means a weaker top 6 than we had last year or the year before, both times that we missed the playoffs. Does Backes at 3C improve the 3rd line enough to offset the drop-off of the top two lines? I really don't think it does, not if it means playing Spooner on the wing, or having Hayes on that line at all.
Disagree.
I think if there are times when CJ wants to play Backes in the Top 6 in certain situations, then that's fine. But a full-time line of Vatrano-Spooner-Heinen would put immense pressure on that Top 6 to produce. They'd fall into the same trap they did last year - a 3rd line that couldn't start in their own defensive zone, and who couldn't be trusted to step on the ice late in close games.
Furthermore, I don't want three kids playing together, picking up each other's bad habits.
It's obviously not ideal to play 3 kids together on that 3rd line, but I don't think that puts any more pressure on the top lines to produce than they already would have...Backes at 3C means a more defensive 3rd line, so the top 6 would have to carry the scoring load anyways, only now with downgraded players. Barring the unavoidable ones, they wouldn't necessarily need to have defensive zone starts at all because that's a legit scoring line, which to me was the real cause for the "trap" they ran into last year -- that line was so tied down with anchors like Hayes that they had trouble producing and that's when the top 6 got exposed. Vatrano-Spooner-Heinen (or Pastrnak if you prefer sticking Backes with Krejci) would be too talented to not produce, even if they are a bit defensively liable.
I guess it really comes down to Spooner and whatever progress he's made. It remains to be seen whether he can be anywhere as close to effective on wing as he is at center, so then you have to figure out what to do with him. As I mentioned to VeddarRants/Bridges31, I think it's a mistake to move him now at this level of value (or in general), and honestly I think it's a mistake to move a player who shows talent at center to wing (Seguin being a great example of why that's not always the best route). Going into his third year, it's time to see what the kid is made of. Pushing him to the wing, or saddling him with a slow defensive type that doesn't fit his playing style doesn't help him at all...give him some actual players and see how it goes.