This.
"Borrowed" powers are the lesser "evil".
If the powers we'd have earned would have been permanent over all the expansions, we'd be in a ridiculous mega OP state right now. Permanent power ups would necessitate something where expansions provide almost nothing beyond stat boost from expansion to expansion, level to level, or risk becoming bloated with new buttons and abilities.
The "borrowed powers" are an expansion gimmick to make us look forward to something more as the expansion unravels, even if those powers are something we've essentially had before, in one form or the other.
This is not an issue. It's something to be celebrated, you muppets.