This may come off as super GM mode but I'd say there would've been around 5m to replace Holl cause I don't see Dubas then making the Ritchie signing at 2.5m while still needing to replace Holl, but we'll never know.
Looking at the depth chart heading into the season Kerfoot was slotted for a 3rd line LW role and he's simply too expensive at 3.5m on a team starving for cap space. We have the in house replacements already at a cheaper cost who can PK like Kampf, Kase, Mikheyev, possibly Engvall? I don't have an issue with Kerfoot at 2m, but he's just not worth his cap hit.
There's no need for me to go in circles, IMO Kerfoot and Holl are interchangeable players and there's no real reason for management to be married to these types considering the playoff failure. Our depth scoring wasn't and isn't great, we had a player there in McCann fairly priced who could've helped in that regard but it was like yeah, whatever take him.
While I agree with you that if they lost Holl, they probably cannot go out and pursue Ritchie.... one of the priorities for the Leafs was to get bigger and grittier up front -- either by resigning Nick Foligno, or replacing him with a player of similar ilk. That's not really Jared McCann's game. Ritchie was likely a prime target for the Leafs and the team likely had far greater expectations for him than he's shown thus far.
As for where Kerfoot slotted in, I don't think the Leafs really went in with defined "numbers" of where the LWers would fit... they had/have Mikheyev, Bunting, Kerfoot, Ritchie & Engvall, with Engvall being the likely 13th forward -- a "sort themselves out" approach. Maybe internally they were thinking looked at Ritchie 1LW, Bunting 2LW, Mikheyev 3LW, and Kerfoot 4LW; but that's only because the other 3 guys have greater offensive upside; whereas Kerfoot is a known quantity. That "known quantity" element to his game makes him a good "match" with a bunch of boom-or-bust guys.
Yes, replace Kerfoot with McCann and you could've confidently slotted McCann into a top 6 role; but McCann doesn't bring what Ritchie can bring, and personally, I don't think it influences the decision to sign Ritchie.
It would however likely had influenced the decision to sign David Kampf... that was a risk the Leafs could afford to take, knowing full well that they had a "backup" 2/3C in Kerfoot should he not work out. McCann is more of a pure winger; so maybe it's not Kampf for $1.5m... maybe it's somebody else for $2m or more. If more than $2m, then you've got less than $2m to replace your top 4 RHD with size.... good luck with that.
Kerfoot was / is an interchangable part at his cap hit. If he were to disappear today, one can probably get a player similar to him with a similar cap hit for a 2nd-3rd round pick type of commitment. The same doesn't hold true for Holl. There wasn't anyone in UFA that was a Holl replacement for $2m....heck, I can't recall too many players being traded this offseason that would be considered "holl-replacements".
TLDR? Even if the Leafs preferred McCann at $2.9m vs Kerfoot at $3.5 (which i think is probably too close to argue definitively)... the "strength of preference" between those was nowhere near the "strength of preference" towards Justin Holl in comparison to the alternatives in that $2m to $2.6m range, even if they used Kerfoot or McCann as bait.
