Eurodollar Futures Pricing

I’m having diffculty understanding the following and could someone help enlighten? Thanks in advance!

Why is it there is difficulty in pricing Eurodollars just because it is an add-on instrument (eg add on with LIBOR). Don’t other instruments also use LIBOR?

Because it’s an add-on rate, the discount rate isn’t known until the expiration of the futures contract.

The pure arbitrage relationship would not hold between a T-Bill (pure discount instrument) and a Eurodollar Futures contract (add on yield).

The simple way to think of this is that you would buy a T-Bill future at say $99 and then it gets delivered to you at expiry for $100 thus your return comes from the fact that you bought it at a discount.

With a Eurodollar future you are contracting to lend/borrow at a time in the future. Therefore at expiry you give someone/borrow $100 and pay/recieve the current rate - and say at expiry you would owe/recieve $101.

There is no way to constuct an arbitrage transactions between these. Very quirky for sure.