But it's been like that ever since Electrum implemented "Batch Unconfirmed Transactions" as well as "Increase Fee (RBF)" features.
The algorithm used is based from RBF's standard which isn't changed ever since.

Your previous experiences may have been on a condition where the fee rate and sizes of the transaction is just right for it to be bumped with additional of 0.2 sat/vB or close.
Like if the first transaction has a single input while the its replacement has to use additional UTXOs to cover the additional output's amount.

For example:
Let's say that you've sent a small size transaction (1 input and 2 output) of 140 vB @ 1sat/vB = 140 satoshi absolute fee.
Then you've sent another transaction right after to batch it with that, but Electrum calculated that it has to use 7 more of your UTXO to cover the additional output's cost:
It'll add about 30vB for the additional output, but since the inputs are now 7, the total size would be: 580vB, the min absolute fee would be 580sat + 140sat = 720sat.
At 720 satoshi absolute fee, the batched txn's fee rate would be: 720 sat ÷ 580vB = 1.24sat/vB.