There is no other "program" as you put it that replaces all of the AmEx Platinum benefits. Each one has its own value and use and if you want to get premium experiences you really need to cobble together your own "program" from multiple sources. There's a ton of content on FlyerTalk about all this.

For example: for domestic lounge access there's nothing comparable to the Platinum card. No other company offers SkyClub, Centurion, Escape, Plaza Premium, AND Priority Pass access for a single very low price. The membership fee alone for all these would be far more than the annual fee of this card even if you didn't use any of the credits at all.

Every credit card travel website sucks - not technically, but in terms of customer service, pricing, availability, etc. So yes, amextravel.com is by far the least technically competent (in terms of performance etc), but they all are sites I would never book anything through when I can avoid it. CapitalOne uses Hopper under the hood, a company that systematically engages in horror story practices to fool people out of money. Chase uses CxLoyalty for this, a company that used to have a decent rep for customer service but I've read many awful stories in recent months about their customer service as well. If having your flight plans messed up and ruining your vacations doesn't matter to you, then sure, those other two cards' websites are at least not horribly slow and badly designed and implemented, but I personally steer clear of using them just as much as I steer clear of amextravel.

Now that AmEx has given up on outsourcing the concierge (for now, as least so it seems), the concierge remains the best of all the cards. That doesn't mean they can do miracles, but I've gotten superb restaurant recommendations for trips that have really added memorable experiences to my trip. They've managed to pull off restaurant reservations at booked up restaurants for me (doesn't always work but even once is a lot better than nothing). I've heard they can be good for getting tickets to some popular shows (Hamilton). I've tried the Chase concierge (Visa Infinite) and the experience was terrible. I would have done much better just searching Yelp and using OpenTable. Also except for FHR you can't get elite status credit booking any hotel with one of these services. So they are no good for hotels (no status credit) and no good for airlines (they mess up bookings).

Chase and CapitalOne only provide Priority Pass. That's it. Chase has a "Luxury Hotels of the World" program which is basically the same as FHR. I don't use it for reasons I will explain below. Hyatt has Privé which is similar but also they charge a lot more so it ends up not really being that good a deal either usually.

AmEx Platinum aldo has the best set of airline transfer partners in my opinion. If you want luxury plane flight travel AmEx is the best/easiest way to get there. However Chase isn't bad, if you put in the work, and it has some decent economy class redemptions.

Where Chase shines is one word: Hyatt. They have by far the best overall customer service and the best value for points in the game, for hotels. So I also have a Sapphire Preferred and a World of Hyatt card and other UR earning cards. It's a terrific program for great hotel travel experiences and getting Globalist status gives you lots of free upgrades and perks with an overall value far better than FHR or similar programs. IHG has also upped their game lately so I have an IHG Premier card as well. But Chase doesn't have good perks in other areas, their lounges are just Priority Pass, etc. Their concierge sucks. And so on.

In the end, unless you want to join Velocity Black or something the best your going to get is to use each card for what it provides and patch together services.