I see. A bank transaction is literally a few lines of text (hopefully over an encrypted connection). Even a heavy bloated website with dumb animations is less than 1 MB download which would not take anywhere near 6 minutes to load.
Also websites optimized for mobile are actually lighter on bandwith, because mobile phones have slow and flaky internet speed, monthly data caps and also have slow processors (if compared to a PC).
I've lived with a 1 Mbit down and 0.5 Mbit up (actual speed) for a while in recent years because I also live in the sticks, so I kind of know how it is.
I really think you either have hardware issues (i.e. the line or modem is unstable) or your ISP is playing stupid games with your connection to convince you to upgrade your contract. You shouldn't have had issues with any of those bandwidths to just access a website.
Being younger than you (my first Internet was an ISDN connection) I know what Internet-based services actually need that. Because I use them. And I can tell you that websites or internet banking are nothing in comparison.
The first is media streaming services, videos and movies like Amazon Prime, Netflix, Youtube and all that, which is what newer generations watch instead than cable (or broadcasted) TV. That's a lot of bandwith, especially at higher quality settings (you got a modern high resolution screen, you want to use it) you are literally downloading a DVD (or more) every time you watch a movie.
The second is playing games and downloading updates for software, which has been on the rise since the 300 baud days. Steam for example is a major game distributor and they only sell games in digital form (i.e. no CD and DVD only download from Internet), the player will have to download sometimes 10GB or even more to install and play the game.
Modern gaming consoles (Playstation and Xbox) are also like that. You buy a disk with your game (sometimes you don't even buy the disk and can buy online directly like with Steam), but then to play it you need to download many GB of updates to it. And every time the developers update a famous game many people will need to use Internet bandwith to download GBs of updates.
There are also "remote gaming" platforms like Google Stadia or Geforce Now, where you are playing a game that is actually run on a remote server. So it's like watching a very high quality movie, and this is VERY intensive for bandwith, only few people with very good connections can use that.
Plus there is file sharing for backup and teamwork and keeping the same files on all your devices automatically, this means you can suddenly have someone uploading GBs of files to many of his devices. Some services for backups like BackBlaze advertise "limitless storage" with their home subscription, and this means people will send them many thousands of GBs of data to keep their data safe in case their house burns down or someone steals their laptop or whatever.
So yeah in the modern day there are plenty of very popular internet services that will need a very high amount of bandwith. Services that back in the day of 300 baud (and even in the times of ISDN) did not exist.
This does not mean that normal websites with text and images suddenly need more resources to do the same things they always did.
In car terms, just because the bridges are strong enough for big trucks does not mean that the cars have also gained weight. It just means that cars are not the bigger vehicle on the road.
There are ways to measure actual bandwith, or at least get an approximation of how much your ISP is lying to you.
Did you try https://www.speedtest.net/ ? It's not 100% accurate but it's good enough for a general estimate.
Also note that bandwith will change in different times as it depends on how many people are using the Internet in your area. If you connect at weird hours at night (and people are asleep) you will usually get better speeds than in the morning (with people at the office) or at the evenings (everyone at home looking at Netflix/Youtube/whatever).
For example, this is my Internet speed at this current moment (yes I have a strange connection with twice as much upload than download speed, let's ignore that for a moment as upload speed is irrelevant in the download test and video) https://www.speedtest.net/result/11123151995
And if I download files from this site https://fastest.fish/test-files (test files for testing purposes, from the "Network Test Files" row) I can download the 5MB and 10MB file instantaneously, and the 20MB file in 2 seconds.
How many pages you can fit in a 5MB document? It's going to be more than 20 pages I think.
That's a silly huge size for a website.
I can also watch a youtube video at 1080p quality and it downloads it fast enough to play from start to finish without stopping to wait for downloading.
For example, let's try watching a youtube video. This is just ambient jazz music, safe for work and all ages https://www.youtube.com/watch?v=Y6VMvfEvzn0 (yes it's technically a static image for the whole video, I know it's dumb and is wasting a ton of bandwith to deliver music that is much much lighter than that) and to make sure you watch at the same quality as me you click on gear icon on the right of the video player box, then you click on Quality, and then click on 1080p60
As an example, that three hour video is around 500 MB in size, nearly a full CD or 1/9 of a DVD or like 400 1.44'' floppy disks.
I also work from home and use Anydesk or Teamviewer or Windows remote desktop to remote-control servers and PCs of clients to install things and solve problems, and it works fine. It's not crazy fast but it's fast enough to work with it.
So that's why I'm saying you shouldn't need more than 100 Mbit unless you know you have specific needs. I can do things very quickly with 30Mbit. Do I need to be able to download that 5Mb file 10 times faster than "instantly"? No I don't.