I very much agree with your assessment. Furthermore, since Catherine (and the Allens) seem not to have any other acquaintances in Bath (Henry Tilney has not made a reappearance), if Isabella is demanding her attention (is also 4 years older than she is, so is more experienced and pushes her points on that score), what else is Catherine really to do but to go along? The fact that Isabella is connected to a brother who is friends with her brother James... there aren't many arguments not to give Isabella a shot, even if she insists on being taken seriously while deceptively chasing young men, etc. Henry Tilney could tease and distinguish between being serious and and pleasing, but one might say that it was perceptive on Tilney's part to see that Catherine was an open-hearted young lady who could be teased and at the same time be responded to in seriousness/earnestness to her own seriousness/earnestness (since Catherine wasn't teasing back.) And Tilney had nothing beyond pleasing manners with which to recommend himself, having no previous connection to Catherine or the Allens.