It seems that inserter upgrades are too good on their own. I'd lock some of them behind more advanced science packs.
I.e., the as follows:

• Drop offset: Red -> Green
• Cross: Red (as is)
• X diagonals Green (as is), and also require fast inserter tech
• Range upgrades: see below

Range upgrades

• Range=2 (3 for long): Blue Science; or Green Science, behind the advanced circuits tech
• Range=3 (4 for long): Yellow Science
• Further upgrades: Yellow & Purple Science

Since it is a change somebody won't like, I'd make this an option in the mod settings called "Expensive researches".
This would also imply the "Range technologies" option.

I'll add this in the next update

I added the new technology with few changes, if you want it more personalized I strongly reccomend editing the technology with an external mod like the modpacks.

I'm not using purple scienze since its "production tech" and does not really fit the scope of smart inserters.