No, I think you are generalizing based on very little evidence.

The seat selection issue is Aer Lingus' policy to discourage use of Online Travel Agencies. You are unlikely to encounter this limitation with US based carriers, but some European lines (e.g. BA) have even less friendly seat selection policies.

The hotel business is fundamentally different. Online Travel Agencies are often selling room nights that they already own, and this can result in inventory or price discrepancies.

I would try again before deciding if cxLoylaty is a good match for your requirements.