I don't think it's as unlikely as you say. Places where R1a is more common than Rib has more pre-Yamnaya EHG ancestry. Most likely there was already R1a in Eastern Europe before steppe breeding and they probably didn't speak IE
Target: Polish

olish16
Distance: 4.6207% / 0.04620698
37.2 Anatolia_Barcin_N
28.6 Yamnaya_RUS_Samara
24.4 RUS_Karelia_HG
9.8 WHG
Target: Russian_Kostroma
Distance: 4.8457% / 0.04845671
26.6 Anatolia_Barcin_N
25.8 Yamnaya_RUS_Samara
25.0 RUS_Chalmny-Varre
17.0 RUS_Karelia_HG
5.6 WHG
In Western Europe where R1b predominates, Yamanya also predominates without deviating to EHG
Target: Irish
Distance: 4.9374% / 0.04937387
49.8 Yamnaya_RUS_Samara
36.4 Anatolia_Barcin_N
13.8 WHG
Target: German:German56
Distance: 5.6763% / 0.05676272
45.0 Yamnaya_RUS_Samara
41.4 Anatolia_Barcin_N
13.6 WHG