You are right... but the method used by oil companied to produce HOBC is quedtionable. They increase RON rating 87 to 95 by adding some meganese based chemical. This meganese is converted into meganese oxide powder within engine cylinder and choke catalytic converter in long run. You can search PW for honda turbo engine issue that lead towards official complaint made by Honda against oil companies in OGRA.
Currently euro5 ron97 by PSO is another thing. This petrol is imp as final finished product from other countries. This has very low maganese level in order to meet EURO5 standard.
Pak suzuki alto is designed for Ron90 by using 1:10 fuel compression ratio. We routine petrol is claimed to be RON 92. So. It can be sufficient for this engine.
HOBC ron95 is for high compression engine with high horse power car like mira eis with 1:11.2 ratio in order to avoid engine knocking.
So in my understanding, mixing of euro5 with normal petrol is sfficient. But driving this alto on euro5 or HOBC may not give much benefits or cost effective and economical.