Who said that philosophers can't identify 'serious' philosophy? I
If they could then there would be some kind of metric. There are plenty of nonsensical and/or completely contradictory philosophies. There are reasons for this, of course. They all boil down to things being "unknowable" though. So philosophers cannot identify serious or "correct" philosophies.
For another, I don't see a problem with imagining that a "respectable" field would be one that you talk about with your friends.
If children were performing science on equal level with tenured professors then yeah I would say it is not exactly respectable. Likewise if my high conversations with friends are indistinguishable from serious topical discussion then it isn't the most respectable.
I guess everything could be defined as "philosophy", in much the same sense that anything can be defined as anything.
That was a complete non-sequitur. Science can be described using philosophy. You might be able to define science as a philosophy but saying science is philosophy is useless.
This whole conversation is about whether science was achieved by philosophy instead of in spite of it. Which you have agreed with. A few philosophers realized they couldn't get meaningful results using traditional philosophy and had to develop better methods. That they were classified as "philosophers" by the context of the time means science no more came from philosophy than it did from theology.