"the price hike could have been a response to slowing sales "
There's absolutely no question about it. Lottery revenue has been generally going downhill for years and the lotteries have been trying to stop the decrease or at least slow it down.
One of the first huge jackpots was when MM reached $656 million in March 2012 on the 18th drawing. It reached 290 on the 16th drawing and then increased 73 > 363 and 293 > 656. A year and a half later in December 2013 it reached $257 million on drawing #18 and the next 4 increases were 34 > 291, 53 >344, 56 > 400, and 248 > $648 million. 2 1/2 years later the jackpot was hit for $508 million on 7/8/2016 with the last increase being a far smaller increase of just $54 million from the previous jackpot of $454 million.
PB first broke $500 million about 8 months after MM did, reaching 587 at 16 drawings on 11/28/12. The final increase was $262 million, from 325. 6 months later PB reached $590 million in May 2013 on the 14th drawing, with a final increase of 240 from 350. The next huge jackpot was the first to make it past $1 billion, reaching 1.586 billion in January 2016. It did that in just 20 drawings, but #17 was only 334 and the next increase was just 194 to 528. The next increase was the first time a lottery rolled after already reaching $500 million and was a whopping 420 to 948. The next increase was the largest ever, increasing by $638 million, but it also made jackpots of less than a billion seem smaller than they had in the past.
The next jackpot to get past $1 billion was the 10/18 MM jackpot of 1.537 billion (advertised as 1.6). It took 23 drawings to reach 548, with subsequent increases of 119 > 667, 333 >1 billion, and 537 > 1.537 (the 26th drawing). Since then there have been 4 jackpots that were bigger. In 2023 MM reached 1.6 billion in August (the 32nd drawing) and PB reached 1.7 in October 36th drawing). PB reached 2/04 billion in November 2022 (41st drawing), and 1.787 this past September (42nd drawing). The biggest increase since 2018 has been $440 million ( the final increase to 2.04 billion) and only 3 increases have been more than $300 million (400 and 440 for the PB record, and 387 for the 9/25 PB).
"There has been considerable criticism of Mega Millions for the slow growth of its jackpot "
Of course we'll have to wait to see how MM grows once it reaches 1 billion, but the last run hit 940 on the 40th drawing. September's PB jackpot was 1.1 billion on the 40th drawing, which is 17% more than the last MM run, but 31% less than PB's 1.6 billion on its 40th drawing on 11/5/22 . With tickets costing 2 1/2 times as much I don't think MM's performance is that far off the PB pace.
"The supported jackpot is $56.1 million whereas in the previous run, the supported jackpot was $53 million "
Although I used annuity values above there can be considerable variation because of changes in interest rates. The current cash value is reported as $36.9 million, versus $35.8 million for the 4th drawing of the previous run. That's an increase of just over 3%. If that trend continues the 10th drawing should be advertised at roughly $144 million depending on interest rates. We've still got a long wait to see how many drawings it will take to reach a billion, assuming it doesn't get hit first.