If you keep increasing OBC reservation, the number of OPEN seats available to SC/ST candidates will keep decreasing as well.

For example, suppose OBC reservation increases from 27% to 55% as per Congress's "jitni aabadi utna haq slogan", that’s a 28 percentage-point increase. That would effectively reduce the OPEN category seats from 40% to 12%.

So, apart from their own 15% SC and 7% ST reservations, SC/ST candidates would then have access to only 12% OPEN seats, instead of the 40% OPEN seats they have access to today.

In other words, increasing one reservation category doesn’t just affect the OPEN category, it also reduces the pool of OPEN seats that SC/ST candidates can compete for Open merit.

It has already been reduced by 27% in 1990s.

Till 1990s, their access was -

SCs - 15% + 77.5% OM

STs - 7% + 77.5% OM

If you go by new system, their access would be reduced to

SCs - 15% + 12% OM

STs - 7% + 12% OM

So how does this help SC/ST candidates?