Every liberal does it too, from center right radlibs to far-right "conservatives": the most extreme right fringe liberals hate the mainstream liberals for not being bigoted enough, the mainstream libs hate the radlibs for not being cruel enough, and the radlibs hate the left for not being chauvinist enough.
Denouncing chauvinism in particular is like a liberal moral event horizon, a cardinal sin against their self-interested belief in the righteousness of the imperial hegemon that keeps the treats flowing at gunpoint.
Ideological liberals despise left-wing shifts because it doesn't gel with their understanding of economics and their broader political values, not because they think leftists have a better politics.
Ideological liberals sure, but they're a minority usually only found in academia and think tanks, if it held for most liberals they wouldn't need to come up with terms like "purity politics" or the "I'm a socialist not communist" discourse you see in progressive liberal circles, Bernie Sander never would have called himself a socialist and become popular if what you're saying was true for the majority
Left-Liberals wouldn't need to come up with clichés like "don't let PERFECT be the enemy of good", that implies these people believe there is a "perfect" and that the leftists they're arguing with hold to it, that's not a fundamental split, at least with social liberals
Frankly the majority of liberals are too uneducated to have fundamental ideological disagreements with us, they don't even understand their own ideology, they have emotional and social disagreements with us grounded in personnel material pressures, but outside the top 20% it's shallow and can be easily broken depending on where they fall in the tax bracket
The "don't let perfect be the enemy of good" refrain was used by left-libs in the context of policy debates like Sanders' healthcare plan vs Warren's. I'd argue that while leftists and left-libs agree on many policies, the differences in what is considered feasible and acceptable (for instance in the 2020 primary, backing Sanders vs Warren) stem from a few ideological differences.
I agree with this. The liberal that feels cognitive dissonance when encountering leftist ideas is on the road to becoming a leftist.