Certainly, some aren’t able to memorize. With work (maybe a lot of work) my experience is that most are able. It is a lost skill. In part, it is no longer common in schools to require memorization. Western cultures are no longer church going people, where memorization of scriptures could occur. I don’t think it has the same emphasis in today’s military.
As to time, again, some may be limited, but most are not. TV, games, social media (ahem), and scrollin ‘ and trollin ‘ consume hours.
“Not on the level.” This has become a terribly misused term. I suppose in this instance it is used to indicate there are those who can’t memorize, and so they would be deprived of the opportunity to serve in office. The underlying premise would appear to be that everyone should have the opportunity to do so, that serving in office is fundamental to being a mason; to being a good freemason. Is that what Freemasonry teaches?
As to reading the ritual, my experience is that it takes rehearsal to do this properly as well. I practice my Masonic speeches and my religious addresses, even though I composed them. How much more then is required with someone else’s words in arcane language for people who, largely, are not familiar with the speech of that era or the Bible. Some of the worst ritual I’ve heard was read.
Sideline corrections are easily taken care of by the presiding officer at the beginning of the meeting. I have done so in more than one body.
All that said, I don’t find memorization to be the sine qua non of Freemasonry. One of the finest ritualists I’ve known is a suspended mason for violating his ob. I’m a member of a side order that delivers its degrees from reading. I’ve also been a grand lecturer in a mouth to ear jurisdiction. In my English chapter and lodge we install from memory.
I simply don’t find this to a determining factor in Freemasonry. But I find the reasoning against memorization to unpersuasive.