The decline in profits predates MTX. MTX were a response to the decline and within 2 years Jagex was seeing record profitability, much of which was clearly owed to MTX since OSRS was just finding its legs.

You want to talk profits vs revenues? Lets look at the annual reports from when Jagex finally bothered to even delineate OSRS from RS3. In 2016 OSRS revenue totaled £24m while Jagex profited £29m. In 2017 OSRS revenue totaled £32m while Jagex profited £44m. In 2018 OSRS revenue totaled £42m while Jagex profited £45m--and that's after the release of OSRS mobile which was undoubtedly a costly project that inflated the game's popularity in a way RS3 has yet to enjoy.

So even if RS3 were carrying OSRS's expenses and the cost of all of Jagex's failed projects and investments in future profitability, it alone could still sustain the company. That holds up if you want to look at this from the angle of RS3's revenue minus Jagex's total expenses, also.

So RS3 would have kept Jagex alive. You lose!