For desktop, a dgpu is the alternative option to an APU, so it certainly is a comparison the end user wants to make. Perhaps not for AMD or their supporters, because it shows just how weak an APU really is for gaming.
Is this trolling? These Apu are not designed as dedicated gaming devices, they just have competent graphics when compared to competitor's products, they are decent enough that if you equip with decent memory and overclock (with standard wraith cooler) you can comfortably play AAA games at low/medium settings...something you can't do with intel products...without buying a dedicated GPU.
You and others arguements/remarks make no sense, AMD does not restrict their Apu to IGP graphics..YOU CAN STILL CONNECT ANY DGPU YOU LIKE...
Gaming..(sub £200)
You put forward a i3-8100..I counter with 2200G/2400G
You counter with i3-8100 + gtx 1030..or even RX 550..
I say R3 1200 + Rx 560 or gtx 1050.
The only combo that can't be beaten for sub £200..is g4560+ 1050Ti.
The closest AMD can get with current products is R3 1200 + Rx 560 4gb.
..which loses a close FPS/£ battle... but offers better all round performance and value long term.
Back on topic, APU Vs APU AMD is the market leader, it offers products with the best all round balance, where you can buy one processor and have a decent experience in productivity and light gaming without breaking the bank...with the option to upgrade in the future or add dgpu if required.
That is picking one specific scenario, ..and not knowing what will happen to R3 1200 prices when 2200g hits...they might well get close to a pentium..
I don't see what your point is, there are no downsides here.