I'd say your offer was fair, but pretty heavily tilted your way. But if he needed a closer and/or 2B and had surplus SP, it would make things a lot more legit. IMO, all trade offers about need and want. I love streaming SP in my 12 team league, so I kinda under-value SP. I am much more likely to trade away a top-5 SP to get a top-15 bats, especially if its at a position of need or scarcity.
In your favor though, I never make my first offer my best offer. The other owner should have countered with a legit offer to see if you were interested in negotiating. His response was bogus.