The problem here is not the actual increase, but the difference between the two initial pensions.
Both pensions are being increased by 10.1%, which is fair.
It's a bit like comparing two workers, one earning 20k and one earning earning 30k. If you give them both a 10% increase (which is fair), the lower paid worker will receive a 2k increase; whilst the higher paid worker will receive a 3k increase. It may seem unfair, but the percentage difference between their salaries remains the same - the higher paid worker still earns 50% more than the lower paid worker and this will be the case for the pensions.
Wrongly or rightly, as already mentioned, pensions were reformed in 2016 and there now appears to be a disparity between the different rates.