its got nothing to do with mempool size..
even if mempool was 500mb but only had 150mb of transactions in there. pools can still deny adding transactions below a threshold. leaving people waiting and needing to RBF to reach whatever threshold mining pools want
so in a 4decades in future scenario when mining pools are going to demand fee's they can just leave the cheap fee tx in mempool to fester for 2 weeks, causing people to RBF upbid their fees to get recognised
I'm not talking about denying . Currently mempool is filled so miners do have to choose , even if they wanted to pass all transactions they can't . This is a condition which can happen with any mempool size . Even with 1 MB miners can deny to add transactions to blocks even if there are higher fees than what would be normal . In fact , it's on their best interest to mine empty blocks as long as subsidy exist . By best interest i mean their chances of finding a block is probably higher with an empty template .
So , without the option of denying , how would a mempool and blocksize increase would affect transaction fees ?
as for leaping to "visa levels"
that debate replaces "scaling" by suggesting the only option is "gigabyte blocks by midnight" to then argue that the network is not ready to even do that. to hope it ends the debate about any type of scaling.. and yea idiots been playing that bait trick for years
the actual scaling is not just "jump blocksize to XX"
its more nuanced
a. punish the frequent spammers: if it costs only them excess fee, they transact less. meaning more genuine people can take the space
b. leaner transactions: punish or prevent bloated transactions, meaning more genuine people can take the space
c. remove the blocksize miscount of 4mb (1mb base+3mb witness) cludge. so that any and all transactions get full utility of the full 4mb space
d. SCALE the blocksize in incremental amounts over time.. no sudden leaps to stupid amounts
So , let's consider a real bussines . If you had a store with a range of customers would you punish the ones that prefer to buy from your store ? And you would try to reward the ones that buy from you occassionaly ?
And what genuine people means ? There are people waiting with their money in hand to have their transactions get into a block . What makes your transaction more genuine than someone else's ?
As for the incremental scaling . There's been 13 years since the launch . 6 years since blocksize wars . I remember Adam Back , Lopp and others saying at that time it was ok to increase it . Right now , according to what most devs believed , blocksize should be at least 32 MB . How big do you think blocksize should be currently ?
ok lets consider a business
lets take some international postal/cargo businesses. for customers wanting to ship a army tank by sea or by air.
..should
everyone pay more for a postage stamp? just because the tank is taking up alot of space.. or should the person trying to send the tank pay a super premium to slide infront of the queue at the ports
why should a tank be able to pay a postage stamp but cause all postage stamps for everyone else to become nearly a hundred dollars for everyone
as for the other stuff about scaling vs leaping.. read what i said and you will understand
right now core devs dont want any scaling/leaping of blocksize bigger then 4mb.. but here is the thing, currently there are other ways to scale onchain to allow more transaction per block before needing to twist their arms to get them to act like bitcoin devs again instead of their other side hustle sponsored projects they prefer
try to read a,b,c,d and you will see how things can be done without having to scream at devs for 'bigger blocks'.. and then when that cludge is sorted then scaling can happen above 4mb
(in short if they have built an ignorance chamber at the 4mb limit. then lets sort out and streamline the 4mb limit)
by the way. you keep talking about gb blocks EG "be like visa"
by the way. you keep talking about 32mb blocks
you keep talking in leaping speak
and its this leaping speak that just makes the debate end because its the same as asking a pregnant woman why dont you give birth to a 6foot tall fully adult son
.. because progressively growing is the logical and most common sense approach. not suddenly birthing large amounts
do you understand scaling yet or will you just reply with another random number
most people want scaling.. so please drop the leaping act. its not helping anyone
and by the way 2009-2013 blocks could only be 0.5mb
and by the way 2013-2016 blocks could only be 1mb
and by the way 2017-now blocks APPEAR as being able to be 4mb. but not all of that 4mb is lean legacy style tx that just do what bitcoin intended
3mb of the 4mb is bloated special scripting witness and other junk that are not even anything to do with signature proofs
so for 6+ years now things have slowed down. even when physical technology has sped up
they say: "but we gave you 3mb extra "bigger blocks", so why still ask for more"
response: "no that 3mb is mainly for junk and new bloaty scripts not even possible pre 2016. however the tx count of 2016 is not even 4x legacy tx count today. not even 2x today not even 1.1x more legacy tx count today, which shows how the so called "extra 3mb" has not actually given people proper scaling to transact more"
amazing logic on his part i must say. 
