BLUF: Trying to figure out load balancing and fail over based on differences of ISP throughput.

There was a reference to a very good Load balance presentation where the presenter showed LB via up or down throughput im Mbps (when reaching specified level switch and when decreases to certain level switch back).

However I was looking at an approx 1.5 difference up and down between my two ISP and wanted to use a RATIO approach. X connections to ISP1 and Y connections to ISP2
Looks like NTh is the way to do this. However its not setup for fractions LOL 1.5/1 (after 1.5 sessions switch ISP for the next session). so it got me thinking why not use 3:2 type ration in Nth.

I just want to make sure my perspective is accurate regarding the following statement: For the first three connections/sessions USE ISP1 and for the next two USE ISP2
So if I use an NTH setup
5:1 go to ISP1
5:2 go to ISP1
5:3 go to ISP1
5:4 go to ISP2
5:5 go to ISP2

Is there a shorter way to do this??
In other words why not have a setup that says
5:4 go to ISP2
5:5 go to ISP2
The rest go to ISP1 (how to say that if possible).

Any guidance appreciated.

5:1 go to ISP1 passthrough =no
5:2 go to ISP1 passthrough =no
5:3 go to ISP1 passthrough =no
To ISP2 passthrough =no

Or

5:4 go to ISP2 passthrough =no
5:5 go to ISP2 passthrough =no
To ISP1 passthrough =no

What happens in NTH if the ISP is not available.

a. ISP1 gateway falls over
b. ISP1 gateway is okay but connection beyond gateway is not available?

The routing rules are already messy with NTH programming.
How to integrate fail over as well...........

Is NTH the best method for my scenario
100/100 and 100/10 service (real world local testing yields 120/110 120/11)

I was initially thinking NTH 3:1, 3:2 Primary and 3:3 secondary OR as post above 5:1-5:3 Primary and 5:4-5:5 secondary.
I was also thinking about a bandwith/throughput approach
When Primary is using >80 download switch to Secondary (back when using <80)
When Primary is using >80 upload switch to Secondary (switch back when using <80)

The only fixed items I can pinpoint at this time are
a. email has to go through ISP2 to send emails........
b. I am putting up video cams that go to cloud servers so that would be upstream and should probably tag to go out Primary (due to 100 up) only when triggered not a full time event.

That packets are marked to go trough a specific gateway. Is the gateway death the your packets will be lost.

If you put a HA in there the it has to be after the NTH. If the target gateway is death then the traffic has be rewritten to go through the other gateway(s).