The result would have been (ridiculously) high fees!!!

mintxfee specifies the minimum (total) fee that your transaction will be created with... NOT the fee rate to be used. So, setting 0.0001 means that if you sent an "average" sized transaction of say 226 bytes, it would still use a fee of 0.0001 BTC... that's 10,000 sats... for a 226 byte transaction, that's a fee rate of just over 44 sats/byte.

Generally, the automatic fee estimation isn't terrible, it just doesn't handle sudden spikes in transaction and/or fee volume very well... it can be quite unpredictable. For that reason, I'd still recommend double checking https://btc.com/stats/unconfirmed-tx and https://jochen-hoenicke.de/queue/#1,24h to get an idea of the current mempool size and "pending" fees before you send a transaction.

If the mempool is low (less than 1 block ie.  less than ~1meg of transactions)... and all the fees are in the 1 sat/byte range, simply using 2 or 3 sats/byte is likely to get nextblock confirmation. If the mempool is getting bigger  (ie. more than 2 or 3 blocks worth, ie. more than ~2meg of transactions) and there are a significant number of transactions using more than 1 sat/byte, you may need to pay a bit more for a fast confirmation.

If it gets really full (like ~10megs+)... expect to see fees spiking up quite high. It's all about "supply and demand"