Negative funding on perps is a rare thing in a bull market. As a short term trade what you are doing might make sense, but you are facing a few big negatives/risks.
- Funding rates might shift to the opposite on a dime.
- You might not get a chance to re-enter with perps at the same or better price after selling on spot.
- You pay fees on every trade you take (decent ones on spot trades).
- Exchange risk that you mentioned yourself.
1] this is not a problem if you check in on the position once a day
2] the price isn't going to change enough in the <60 seconds it takes to do this to matter
3] fees on MEXC are almost nonexistent and huge orders can be reduced to zero using maker limit orders. My trading fee on $2400 was 30 cents.
4] Worth repeating over and over again. Counterparty risk can not be overstated.